Ingredients

Cake:

1 cup unsalted butter, softened, more for greasing the pans

3 1/4 cups cake flour, more for dusting the pans

1 tablespoon baking powder

1 teaspoon salt

2 2/3 cups granulated sugar

5 large eggs, at room temperature

4 large egg yolks, at room temperature

2/3 cup vegetable oil

1 tablespoon grated orange zest

2 teaspoons vanilla extract

1 cup buttermilk, at room temperature

For the orange syrup

1 cup freshly squeezed orange juice

1/4 cup granulated sugar

Filling:

1 (12-ounce) jar orange marmalade

Frosting:

1 cup heavy cream, chilled

4 tablespoons granulated sugar

1 cup sour cream, chilled

Preparation

Cake: Sift flour, baking powder, & salt twice in a large bowl. In a separate bowl, beat butter on MEDIUM (~4 minutes). Add sugar steadily with mixer running; beat until light & fluffy. Add eggs & yolks, one at a time, beating well after each addition; scrape down sides at least once. After eggs are added, continue to beat on MEDIUM for 2 minutes; add oil & beat for 1 minute on LOW. In a third bowl, combine orange zest, vanilla, & buttermilk. Using a rubber spatula, fold in half of dry ingredients. Scrape down sides of bowl, add half of the buttermilk mixture - repeat.

Pour batter in pans, smooth surface, rap on counter, & place in oven. Bake for 30-35 minutes, or until a toothpick inserted into center comes out clean. Let cakes cool in pans on racks for 20 minutes.

Orange syrup: In small bowl, stir together orange juice & sugar until dissolved. While cakes are still in pans, use a toothpick or skewer to poke holes at 1/2-inch intervals in the cake layers. Spoon syrup over each layer, allowing syrup to be completely absorbed before adding the remainder. Let layers cool completely in pans.

Filling: Heat marmalade in a small saucepan over medium heat until just melted. Let cool for 5 minutes.

Frosting: In a chilled mixing bowl, whisk heavy cream with sugar until stiff peaks form. Add sour cream SLOWLY & whisk until mixture is a spreadable consistency.

Cake assembly: Invert one layer on a cake plate & peel off parchment. Spread 1/3 of marmalade over top, smoothing into an even layer; repeat with second layer. Place third cake layer on top, remove parchment, & spoon remaining marmalade onto the center, leaving a 1.25-inch border around the edges. Frost sides & top border, leaving the marmalade on top of the cake exposed. Or, frost entire cake first, adding the marmalade as a garnish on top.

Chill for at least 2 hours before serving.