Step 1: Bake the Cake Layers Preheat your oven to 350°F (177°C). Grease two 8-inch cake pans, dust with flour, and line the bottoms with parchment paper. In a large bowl, combine the sugar, vegetable oil, melted butter, eggs, egg yolks, and vanilla until light and well mixed. Blend in the sour cream or Greek yogurt.

Step 2: Mix Dry and Wet Ingredients In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Alternately add half of the dry mixture and half of the buttermilk (or milk) to the wet ingredients, mixing just until incorporated. Stir in the sprinkles by hand to avoid crushing them.

Step 3: Bake and Cool Divide the batter evenly between the prepared pans. Bake for 25 to 32 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for 15 minutes, then transfer them to a wire rack to cool completely.

Step 4: Assemble the Ice Cream Layers Soften your ice cream for 15 to 20 minutes at room temperature it should be spreadable but not melted. Level the cake layers by slicing off the domed tops to create flat surfaces. Line an 8-inch springform pan with plastic wrap and place a cake board at the bottom for easy removal.
Place one cake layer in the pan, spread the softened ice cream evenly over it, then top with the second cake layer inverted so the flat side faces up. This creates a smooth, level top for frosting.

Step 5: Freeze and Frost Wrap the assembled cake twice with plastic wrap and freeze for 2 to 4 hours, or until solid. Meanwhile, chill your mixing bowl and beaters. Whip the heavy cream until soft peaks form, then gradually add powdered sugar and sprinkles. Continue whipping until stiff peaks develop. Transfer to a piping bag.
Remove the cake from the pan, unwrap it, and frost the edges and top smoothly with the whipped cream. Decorate with extra sprinkles and any remaining frosting. Refreeze for 30 to 60 minutes before serving.