Start by greasing or lining a 9×13 inch baking pan and preheating your oven to 325°F. Toss your sprinkles with a little flour to stop them from sinking to the bottom of the cake.

Whisk the flour, baking powder, baking soda, and salt in a bowl to prepare the crucial base that ensures a flawless cake crumb.

In a separate bowl, beat the butter, sugar, oil, and vanilla until the mixture becomes lighter in color and fluffy, this usually takes about 4 minutes.

Add the egg yolks one at a time, mixing well and scraping down the sides to keep everything smooth.

Begin incorporating the dry ingredients and milk one after the other, mixing delicately each time. Stir in the sour cream to keep the cake moist and tender.

Whip the egg whites until soft peaks form, meaning they hold their shape but still bend slightly, and fold half of them gently into the batter to keep it airy.

Slowly incorporate the rest of the mix and the flour-coated sprinkles, folding until just unified.

Pour the batter evenly into your pan, smooth the top, and bake for about 40 minutes. Check for doneness by inserting a toothpick; it should emerge clean or with just a few moist crumbs.

Give the cake some time to cool in the pan before lifting it onto a wire rack.