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 damp sand.
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 ½ minutes, to aerate the batter and build the cake’s structure.
Divide the batter equally between 32 wells of a cupcake pan.
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.