- 3 1/4 cups cake flour (not self-rising), sifted
- 2 teaspoons baking powder
- 1 teaspoon coarse salt
- 8 ounces (2 sticks) unsalted butter, softened
- 1 3/4 cups sugar
- 2 vanilla beans, split and scraped, pods reserved for another use, or 1 tablespoon pure vanilla extract
- 1 cup whole milk
- 8 large egg whites, room temperature
- 1 1/2 pints (3 cups) blueberries
- 34 raspberries (1/2 pint; about 1 1/3 cups)
- Seven-Minute Frosting (http://www.marthastewart.com/283495/seven-minute-frosting)
- Preheat oven to 325 degrees, with racks in middle and lower positions. Line 3 muffin tins with 34 liners. Whisk together 3 cups flour, the baking powder, and salt.
- Beat butter, 1 1/2 cups sugar, and the vanilla until pale and fluffy. Scrape down sides of bowl as needed. Beat in flour mixture in 3 additions, alternating with milk.
- Beat whites until soft peaks form. Gradually add remaining 1/4 cup sugar, beating until stiff, glossy peaks form. Using a rubber spatula, fold one-third of the whites into batter, then carefully fold in remaining whites. Gently toss blueberries with remaining 1/4 cup flour to coat. Gently fold floured blueberries into batter. Divide batter evenly among cupcake liners.
- Bake until cupcakes spring back when touched, 23 to 25 minutes. Let cool in tins on wire racks for 10 minutes. Remove cupcakes from tins, and let cool completely on wire racks. Frost cupcakes and garnish each with a raspberry.
Use a light-colored metal muffin tin for this recipe. Dark and nonstick tins retain too much heat and will cause the cupcakes to burn around the edges before cooking completely in the middle.