one 18-by-13-inch sheet pan or two 8-inch round cake pans
Preheat the oven to 335 degrees F. Grease one 18-by-13-inch sheet pan or two 8-inch cake pans with cooking spray and line the bottoms with parchment. Spray the parchment.
Sift the cake flour, sugar, baking powder, salt and baking soda into the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed for 30 seconds.
Whisk together the melted butter, sour cream, buttermilk, oil, eggs, egg yolk, vanilla and the orange zest in a medium bowl.
Add half of the wet ingredients to the dry and mix on low until a smooth paste forms. Stop to scrape down the bowl and paddle with your spatula. Add the remaining wet ingredients on low speed. Once combined, increase the speed to medium and beat for 1 full minute. Stir in the sprinkles.
Pour the batter into the prepared sheet pan, or if using two 8-inch cake pans, divide the batter between the two pans, about 26 ounces in each.
Bake until a toothpick inserted in the centers comes out with some moist crumbs adhering, 28 to 32 minutes for the 8-inch round cakes and 25 to 30 minutes for the 18-by-13-inch sheet cake. Cool in the pan or pans for 10 minutes, then turn the cake or cakes out onto a cooling rack to cool completely, about 1 hour.