Preheat oven to 350°F. Grease and line round pans. Mix together all dry ingredients (flour, baking powder, baking soda and cornstarch, sugar, and salt) in a stand mixer with a paddle until fully combined.
Melt butter and slowly add into the dry mix, on low speed. Continue to mix until no butter remains, and the mixture becomes crumbly. Pour in eggs, one at a time and mix on low until incorporated.
Mix in oil, yogurt and buttermilk in two installments, on low speed. Add in vanilla and mix at low speed until everything is fully incorporated.
Scrape down the sides of the bowl with a spatula, then beat on medium high for an additional 20-30 seconds.
Add sprinkles to your batter and incorporate into the batter evenly.
Evenly divide that batter between the three round cake pans. If you only have two cake pans pour cake mixture into coated cakes pans and bake your cakes in batches.
Bake for 35-40 minutes, or until a skewer comes out clean.
Allow to cool for 10 minutes, then run an offset spatula around the perimeter of the pan to separate the cake from the pan. Place cake layers on wire rack to finish cooling.
Tip: For a moist and tender cake, avoid overmixing the batter and don't overbake the layers.
