In a medium bowl, sift the flour, cornstarch, baking powder, baking soda, and salt. Set aside.
1 3/4 cup All-purpose flour, 1 TBSP Cornstarch, 1 tsp Baking powder, 1/4 tsp Baking soda, 1/2 tsp Salt
Using a mixer, beat the oil and sugar on high speed for 2 minutes. It will become pale and fluffy.
1/2 cup Oil, 1 cup White granulated sugar
Add in the vanilla, sour cream, and eggs and mix on medium speed until combined. Scrape the bowl.
1 TBSP Pure vanilla extract, 1/4 cup Sour cream, 2 Large eggs
Add in the dry ingredients and buttermilk. Mix on low speed until just combined. Take the bowl off the mixer and mix using a baking rubber spatula. Add in the sprinkles.
1/2 cup Buttermilk, 1/3 cup Rainbow jimmie sprinkles
Spread the cake batter first on the bottom of the prepared pan. Spread the cheesecake batter on top of the cake batter. Spread evenly.
Bake for 55-65 minutes until the cheesecake in the middle has a slight jiggle. Keep the cheesecake in the pan, and place on a cooling rack to cool completely.
Cover the pan with foil and chill in the fridge for at least 6 hours or overnight.