Preheat the oven to 350 degrees F.

Place the sugar, all-purpose flour, cake flour, cocoa, baking powder, baking soda, and salt in a large mixing bowl and stir to combine.

Mix in the butter on low speed, until the mixture resembles moist crumbs.

Stir in the eggs, one at a time, scraping the bottom and sides of the bowl with a silicone spatula after each addition. Add the Greek yogurt and vanilla, scraping the bottom and sides of the bowl to be sure all the ingredients are well-combined. Beat on medium speed for 1 to 1 1/2 minutes, to aerate the batter and build the cake’s structure.

Fill lined cupcake wells just over half full (approx. 1/4 cup of batter).

Bake for 15 minutes, or until a cake tester inserted in the center of a cupcake comes out clean or with moist crumbs.

Cool completely before frosting.