Preheat the oven to 350° F. Place the cake flour, all-purpose flour, sugar, baking powder, and salt in a mixing bowl and stir to combine.
STEP 2
Add the butter and mix on low speed, until mixture resembles coarse crumbs (4 to 5 minutes).
STEP 3
Add the eggs, one at a time, and scrape the bottom of the bowl to make sure all the ingredients are well-combined.
STEP 4
4. Combine the milk and vanilla in a measuring cup. Beat half this mixture into the flour mixture. Beat on medium speed for 1½ minutes, scrape the bottom and sides of the bowl, add the remaining milk mixture, and beat for another 30 seconds.
STEP 5
5. Fill paper liners ⅔ of the way with batter, and bake for 20 minutes, or until a toothpick inserted in the centre of the cupcake comes out clean. Cool completely before topping with buttercream.