Preheat oven to 325 degrees. Line cupcake pans with paper liners; set aside. In the bowl of an electric mixer fitted with the paddle attachment, combine flours, sugar, baking powder, and salt; mix on low speed until combined. Add butter, mixing until just coated with flour.
In a large glass measuring cup, whisk together eggs, milk, and vanilla. With mixer on medium speed, add wet ingredients in 3 parts, scraping down sides of bowl before each addition; beat until ingredients are incorporated but do not overbeat.
Divide batter evenly among liners, filling about 2/3 full. Bake, rotating pan halfway through, until a cake tester inserted in the center comes out clean, 17 to 20 minutes.
Transfer to a wire rack to cool completely. Repeat process with remaining batter. Once cupcakes have cooled, use a small offset spatula to frost tops of each cupcake. Decorate with sprinkles, if desired. Serve at room temperature.
Basic Vanilla Buttercream
1 cup (2 sticks) unsalted butter, room temperature
6 to 8 cups confectioners’ sugar
1/2 cup milk
1 teaspoon pure vanilla extract
In the bowl of an electric mixer fitted with the paddle attachment, cream butter until smooth and creamy, 2 to 3 minutes. With mixer on low speed, add 6 cups sugar, milk, and vanilla; mix until light and fluffy. If necessary, gradually add remaining 2 cups sugar to reach desired consistency.