Roasted Beef Tenderloin with French Onions and Horseradish Sauce

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There’s something undeniably elegant about a perfectly roasted beef tenderloin. With its buttery texture, rich flavor, and tender center, this dish transforms any dinner into a celebration. The slow caramelization of French onions alongside the beef creates a savory-sweet contrast, while the bold horseradish sauce cuts through with just the right amount of creamy heat. Whether you’re hosting a dinner party or preparing a memorable holiday meal, this recipe is the showstopper you’ve been searching for.

The star here is a center-cut beef tenderloin, seared to develop a crust and then oven-roasted to medium-rare perfection. Paired with golden onions cooked low and slow until they’re jammy and sweet, it’s a flavor-packed combo that needs no complicated sides to shine. The creamy horseradish sauce adds an elevated touch that brings balance and brightness to each bite. This is classic comfort food with a gourmet twist.

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Why You’ll Love This Roasted Beef Tenderloin with French Onions and Horseradish Sauce

• Melt-in-your-mouth tenderloin that’s juicy and deeply flavorful.
• Perfectly caramelized French onions to complement the beef’s richness.
• Easy yet elegant — it looks restaurant-worthy but is surprisingly simple to pull off.
• Make-ahead friendly — the horseradish sauce can be prepped a day in advance.
• Naturally low-carb and gluten-free, ideal for a variety of dietary preferences.
• Impressively festive, making it perfect for special occasions, holidays, or romantic dinners.
• Balanced flavor — from the savory beef to the sweet onions and punchy horseradish, every bite is layered with contrast.
• Minimal cleanup thanks to one-pan roasting.

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Preparation Phase & Tools to Use (Essential Tools and Equipment, and the Importance of Each)

Roasting a beef tenderloin to perfection begins long before it hits the oven. Careful preparation and the right tools make all the difference in ensuring your dish is beautifully seared, evenly cooked, and served at its peak. Here’s what you’ll need and why it matters:

• Cast Iron Skillet or Heavy Oven-Safe Pan
  Essential for developing that golden-brown crust during searing and transitioning seamlessly into oven roasting without losing heat retention.
• Meat Thermometer (Digital or Instant-Read)
  This is your best friend for nailing the internal temperature. Since tenderloin can quickly shift from medium-rare to overcooked, a thermometer ensures precision.
• Chef’s Knife & Cutting Board
  For trimming the tenderloin and slicing it cleanly after resting — a sharp knife prevents tearing and helps present the meat attractively.
• Tongs
  Ideal for searing all sides of the tenderloin without piercing the meat and letting the juices escape.
• Aluminum Foil or Butcher’s Twine
  Twine helps the roast hold a uniform shape for even cooking. Foil is key for tenting the meat after roasting, allowing it to rest and retain juices.
• Medium Saucepan (for Horseradish Sauce)
  Used to warm and mix your creamy sauce base without curdling or breaking the consistency.
• Baking Sheet or Roasting Pan
  Holds your onions and tenderloin together as they roast, letting the beef juices mingle with the onions for added flavor.

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Preparation Tips

• Bring the beef to room temperature
  Let the tenderloin sit out for 30–45 minutes before cooking. This helps it cook more evenly and prevents a cold center.
• Trim the silver skin
  Use a sharp knife to remove the tough, silvery membrane from the tenderloin. It doesn’t break down during cooking and can make the meat chewy.
• Tie it up
  Use butcher’s twine to tie the tenderloin at 1.5-inch intervals. This ensures even thickness for consistent cooking.
• Pat dry before seasoning
  Removing excess moisture helps create a better sear. Then season generously with kosher salt and cracked black pepper.
• Use high heat for the sear
  Start with a blazing hot skillet to develop that signature crust — this locks in the juices before roasting.
• Deglaze if needed
  After searing, consider a splash of broth or wine in the pan to scrape up those browned bits — instant flavor for your onions.
• Make the horseradish sauce ahead
  It improves in flavor as it sits, and you’ll have one less thing to worry about while the meat roasts.

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Ingredients for This Roasted Beef Tenderloin with French Onions and Horseradish Sauce

This dish balances bold flavors with minimal, quality ingredients. Here’s everything you’ll need, organized by component for ease:

For the Beef Tenderloin

• 1 whole center-cut beef tenderloin (about 2.5 to 3 lbs), trimmed and tied
• 2 tablespoons olive oil
• 2 teaspoons kosher salt
• 1 teaspoon freshly cracked black pepper
• 3–4 sprigs fresh thyme
• 2 cloves garlic, minced
• 1 tablespoon unsalted butter

For the French Onions

• 3 large yellow onions, thinly sliced
• 2 tablespoons olive oil
• 1 tablespoon butter
• 1/2 teaspoon salt
• 1/4 teaspoon black pepper
• 1/2 teaspoon sugar (optional, helps boost caramelization)

For the Horseradish Sauce

• 1/2 cup sour cream
• 2 tablespoons prepared horseradish (more or less depending on heat preference)
• 1 teaspoon Dijon mustard
• 1 tablespoon fresh lemon juice
• 1 tablespoon chopped fresh chives or parsley
• Salt and pepper to taste

Optional: Add a splash of cream for a silkier horseradish sauce or a pinch of smoked paprika for depth.

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Step 1: Prep the Beef Tenderloin

Start by removing the tenderloin from the fridge and allowing it to come to room temperature for 30–45 minutes. Trim any silver skin using a sharp knife, then tie the roast with butcher’s twine every 1.5 inches to maintain even shape. Pat dry with paper towels and season generously with salt and freshly cracked black pepper.

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Step 2: Caramelize the French Onions

While the beef is resting, heat a large skillet or cast iron pan over medium-low heat. Add 2 tablespoons of olive oil and 1 tablespoon of butter. Add the sliced onions, salt, pepper, and optional sugar. Stir occasionally, cooking low and slow for 25–30 minutes, until deeply golden and soft. Transfer onions to a roasting pan.

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Step 3: Sear the Tenderloin

Increase heat to high and return the skillet to the stovetop. Add 2 tablespoons olive oil. Once the oil is shimmering, sear the tenderloin for about 2 minutes per side until a deep brown crust forms. Add the minced garlic and butter during the last minute, basting the meat with the melted butter and garlic.

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Step 4: Roast the Tenderloin

Preheat the oven to 425°F (220°C). Place the seared tenderloin on top of the bed of caramelized onions in a roasting pan. Add fresh thyme sprigs on top. Transfer the pan to the oven and roast for 20–25 minutes or until the internal temperature reaches:

• 120°F (49°C) for rare
• 125°F (52°C) for medium-rare
• 130°F (54°C) for medium

Use a meat thermometer for accuracy.

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Step 5: Rest the Meat

Remove the pan from the oven and transfer the tenderloin to a cutting board. Tent loosely with foil and let it rest for 15 minutes. This step is critical for juicy slices.

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Step 6: Make the Horseradish Sauce

While the meat rests, mix the sour cream, horseradish, Dijon mustard, lemon juice, and chopped herbs in a bowl. Taste and season with salt and pepper as needed. Chill until ready to serve.

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Step 7: Slice and Serve

Slice the rested tenderloin into ½-inch thick medallions. Serve over the bed of caramelized onions with a generous spoonful of horseradish sauce on the side or drizzled over the top.

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Notes

• Resting is non-negotiable: Letting the beef rest after roasting ensures that the juices redistribute evenly, giving you tender, moist slices every time. Cutting too early will lead to dry meat.
• Customize the horseradish sauce: Adjust the horseradish quantity based on how spicy you want the sauce. Start with less, then add more to taste — it can get fiery fast!
• Use the pan drippings: Don’t discard the roasted onions and leftover juices in the pan — they’re liquid gold. Spoon them over the sliced beef for added richness and depth.
• Make it ahead-friendly: You can caramelize the onions and make the horseradish sauce a day ahead. Just reheat the onions gently and serve the sauce chilled.
• Choose the right tenderloin cut: A center-cut tenderloin is ideal — uniform in shape and easy to roast evenly. Ask your butcher to trim it if you prefer less prep.

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Watch Out for These Mistakes While Cooking

• Skipping the meat thermometer
  Guesswork will ruin a high-quality tenderloin. Always use a thermometer to check doneness. Even a few degrees can make or break it.
• Not tying the tenderloin
  Without twine, the roast may cook unevenly, leading to overdone tips and an undercooked center. Tying it ensures even thickness throughout.
• Overcrowding the onions
  When caramelizing, give the onions space. If you pile them too high in the skillet, they’ll steam instead of slowly brown.
• Searing in a cold pan
  A proper sear only happens in a hot pan. Wait until the oil shimmers before adding the beef.
• Skipping the rest time
  This is crucial. Cutting into the roast immediately will make all those flavorful juices run out onto the board instead of staying in the meat.
• Overcooking the beef
  Tenderloin has very little fat — once it passes medium, it can turn dry and leathery. Pull it early and let carryover heat do the rest.
• Using raw horseradish
  Prepared horseradish is key here. Raw horseradish root is extremely pungent and not ideal unless you’re making your own sauce from scratch.
• Not seasoning enough
  Tenderloin is mild in flavor, so be generous with salt and pepper before searing. It helps build that bold outer crust.

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What to Serve With Roasted Beef Tenderloin with French Onions and Horseradish Sauce

A dish this rich and elegant deserves thoughtful pairings that highlight its flavor without stealing the spotlight. Whether you’re building a festive holiday table or an intimate dinner menu, the right sides will elevate the whole experience.

8 Recommendations:

1. Garlic Mashed Potatoes

Creamy and buttery with a subtle garlic punch — the perfect canvas to soak up the horseradish sauce and beef drippings.

2. Roasted Brussels Sprouts with Balsamic Glaze

Their slight bitterness and caramelized crunch balance beautifully against the sweetness of the onions and richness of the beef.

3. Gratin Dauphinois (French Scalloped Potatoes)

A luxurious, cheesy potato side that complements the tenderloin’s refined character — perfect for special occasions.

4. Honey-Glazed Carrots

Tender, sweet, and colorful — these bring brightness and a subtle contrast to the deep flavors of the dish.

5. Creamed Spinach

A velvety green side with just the right earthiness and creaminess to echo the horseradish sauce.

6. Crispy Smashed Potatoes

Golden and textured with crunchy edges — ideal if you want something rustic yet indulgent.

7. Buttered Green Beans with Almonds

A simple, fresh option that adds crunch and color without overwhelming the plate.

8. Warm Dinner Rolls or Popovers

Perfect for mopping up all the juices, onions, and sauce. Popovers offer a fancier feel, while rolls keep it classic.

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Storage Instructions

This dish stores surprisingly well and makes for elegant leftovers — if you have any!

• Refrigeration
  Store leftover sliced tenderloin in an airtight container in the fridge for up to 4 days. Keep the caramelized onions and horseradish sauce in separate containers to preserve their texture and flavor.
• Freezing
  While beef tenderloin can be frozen, it’s best to do so before it’s sliced. Wrap it tightly in plastic wrap and foil, then freeze for up to 2 months. Thaw in the refrigerator overnight and reheat gently to maintain texture. Avoid freezing the horseradish sauce — dairy-based sauces tend to separate.
• Reheating
  Warm sliced beef gently in a 250°F (120°C) oven, covered with foil, for about 10–15 minutes. You can also sear quickly in a hot skillet for 1 minute per side to revive the crust. Reheat onions in a skillet over low heat with a touch of butter. Serve horseradish sauce cold or allow it to come to room temperature.

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Estimated Nutrition

Based on one serving (1/6 of the full recipe, including beef, onions, and 1 tablespoon of horseradish sauce)

• Calories: ~410 kcal
• Protein: 38g
• Fat: 25g
  • Saturated Fat: 10g
• Carbohydrates: 8g
  • Sugars: 4g
  • Fiber: 1g
• Cholesterol: 110mg
• Sodium: 580mg

Nutritional values may vary based on portion size and specific ingredients used.

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Frequently Asked Questions

1. Can I make this dish ahead of time?

Yes! You can prep the horseradish sauce and caramelized onions a day ahead. The tenderloin is best cooked fresh, but you can trim, tie, and season it in advance and keep it in the fridge until ready to sear and roast.

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2. What’s the ideal doneness for beef tenderloin?

Medium-rare (125°F / 52°C) is the sweet spot — tender, juicy, and flavorful. If you prefer more doneness, don’t go past medium (130°F / 54°C), as tenderloin can dry out quickly.

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3. Can I use a different cut of beef?

You can substitute with sirloin roast or eye of round for a more budget-friendly option. However, these cuts are leaner and may require marinades or slower cooking methods for tenderness.

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4. What kind of horseradish should I use?

Use prepared horseradish, found in jars in the refrigerated section. Avoid horseradish “sauce” (which may already contain cream or mayo) unless you’re adjusting the recipe accordingly.

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5. Can I grill the tenderloin instead of roasting it?

Absolutely. After searing, transfer to indirect heat on the grill and cook covered until the desired internal temperature is reached. Rest as usual before slicing.

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6. How do I keep the tenderloin from overcooking?

Monitor the internal temp with a digital meat thermometer and pull the roast 5°F before your target doneness. The meat will continue cooking slightly while resting.

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7. Is this recipe gluten-free?

Yes, it’s naturally gluten-free. Just ensure your horseradish and Dijon mustard are certified gluten-free if you’re serving guests with sensitivities.

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8. Can I make this without a cast iron skillet?

Yes, any heavy-bottomed oven-safe skillet or stainless steel pan will work. Just avoid non-stick pans — they don’t achieve a proper sear.

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Conclusion

Roasted Beef Tenderloin with French Onions and Horseradish Sauce is the kind of recipe that turns a good dinner into an unforgettable one. With its buttery texture, deep umami from the slow-cooked onions, and the bold contrast of creamy horseradish, this dish is luxurious without being fussy. It’s tailor-made for holidays, celebrations, or whenever you’re ready to impress.

Whether you’re hosting a crowd or treating yourself to a refined homemade meal, this tenderloin delivers on flavor, elegance, and simplicity. Once you’ve made it, it just might become your go-to for every special occasion.

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