1. Preheat oven to 350°F (175°C) and thoroughly grease and flour a 10–12 cup bundt pan.

2. In one bowl, whisk together flour, baking powder, baking soda, and salt. Divide the mixture in half. Add cocoa powder to one half and whisk.

3. In a large mixing bowl, cream butter and sugar together until light and fluffy.

4. Beat in eggs one at a time. Mix in orange zest, orange juice, vanilla, and yogurt (or sour cream).

5. Divide wet batter evenly between two bowls. To one, add plain flour mix; to the other, add cocoa flour mix and milk. Mix each until just combined.

6. Spoon the batters alternately into the pan, then gently swirl with a knife to marble.

7. Bake for 45–55 minutes, or until a skewer comes out clean. Cool in the pan for 15 minutes, then invert onto a rack.

8. To make the glaze, heat cream until steaming, pour over chocolate, let sit for 1 minute, then stir until smooth.

9. Once the cake is cool, drizzle the glaze over the top. Garnish with orange zest curls if desired.