for the cupcakes
1 3/4 cups all-purpose flour
1 1/2 teaspoons baking powder
3/4 teaspoons table salt
1 cup granulated sugar
1 1/2 sticks unsalted butter, softened but slightly cool, cut into 12 pieces
3 large eggs
3/4 cups milk
2 teaspoons vanilla extract
for the frosting
4 large egg whites
1 1/4 cups sugar
1 1/2 cups (3 sticks) unsalted butter, room temperature, cut into tablespoons
1 teaspoon pure vanilla extract
1 1/2 cups macerated strawberries, pureed in a food processor
For the cupcakes: Preheat oven to 350F. Line a standard muffin pan with paper baking cups.
In the bowl of a stand mixer, combine the flour, baking powder, salt, and sugar on low speed. Add the butter, 1 piece at a time, and combine until the mixture resembles coarse sand. Add the eggs, 1 at time, and mix until fully combined. Add the milk and vanilla extract, increase the speed to medium, and mix until the batter is light, fluffy and free of lumps.
Fill the lined muffin cups three-quarters full, being careful not to overfill. Bake until a toothpick inserted in the center of the cupcake comes out clean, about 18 to 20 minutes. Cool the cupcakes in the pan for 5 minutes, then transfer to a wire rack to cool completely.
For the frosting: In the heatproof bowl of an electric mixer set over a saucepan of simmering water, combine egg whites and sugar. Cook, whisking constantly, until sugar has dissolved and mixture is warm to the touch, but not hot.
Attach the bowl to the mixer fitted with the whisk attachment. Beat the egg-white mixture on high speed until it holds stiff peaks. Continue beating until the mixture is fluffy and cooled, about 6 minutes. Switch to the paddle attachment. With mixer on medium-low speed, add butter several tablespoons at a time, beating well after each addition. (If frosting appears to separate after all the butter has been added, beat on medium-high speed until smooth again, 3 to 5 minutes more.) Beat in vanilla. Beat on lowest speed to eliminate any air bubbles, about 2 minutes. Stir in macerated strawberries with a rubber spatula until frosting is smooth.
Decorate cupcakes as you desire; in this case, with frosting and blue sprinkles for the Fourth of July.