1. Preheat oven to 350°F (175°C) and line a 9×13-inch baking pan with parchment paper.

2. In a large bowl, combine flour, sugars, cinnamon, and salt. Cut in cold butter using a pastry cutter until crumbly.

3. Press two-thirds of the mixture into the bottom of the prepared pan to form the crust. Reserve the rest for the topping.

4. Bake the crust for 12–15 minutes until lightly golden, then let cool slightly.

5. In a medium bowl, toss apple slices with sugars, flour, cinnamon, nutmeg, lemon juice, and vanilla until evenly coated.

6. Spread the apple mixture evenly over the pre-baked crust.

7. Sprinkle the remaining crumble mixture over the apples and gently press it down.

8. Return to oven and bake for 35–40 minutes, until the topping is golden and apples are bubbling.

9. Meanwhile, make the caramel: In a small saucepan, combine sugar and water over medium heat until it turns deep amber.

10. Remove from heat, carefully whisk in heavy cream, then stir in peanut butter, salt, and vanilla until smooth.

11. Let bars cool completely in the pan—about 2 hours.

12. Lift out with parchment and cut into squares.

13. Drizzle with cooled peanut butter caramel before serving.

14. Sprinkle with flaky sea salt if desired.