Preheat the oven to 350°F. Line a 24-cup cupcake pan with cupcake liners.
Whisk dry ingredients together and set aside.
2½ cup All-purpose flour, 3 teaspoon Baking powder, 1 tablespoon Corn starch, ½ teaspoon Salt
In a measuring cup, mix the milk and the buttermilk. Set aside.
1 cup Milk, ¼ cup Buttermilk
Using a sand mixer set on the whisk attachment, cream the sugar, oil, eggs, and vanilla extract until light and fluffy. About 5 minutes.
3 Eggs, ½ cup Oil, 1 tablespoon Clear Vanilla extract, 2 cups Sugar
Add the sour cream and mix until just combined.
½ cup Sour cream
Using a spatula, add the flour alternating with the milk mixture. Starting and finishing with dry ingredients. DO NOT OVERMIX.
Bake for 15-17 minutes or until an insert comes out clean. Let cool in the pan for 10 minutes, then transfer to the cooling rack. Frost with the desired frosting.