01 - Preheat oven to 350°F. Line a standard 12-cup muffin tin with decorative liners.
02 - In a mixing bowl, whisk together the all-purpose flour, baking powder, and salt until well blended.
03 - In a separate bowl, beat softened butter and granulated sugar until pale and fluffy. Add eggs one at a time, mixing thoroughly after each addition. Incorporate vanilla extract.
04 - Alternately add the flour mixture and whole milk to the butter mixture, beginning and finishing with flour. Mix gently until just incorporated.
05 - Evenly divide batter between cupcake liners. Bake for 18 to 20 minutes, or until a toothpick inserted into the center emerges clean. Allow cupcakes to cool completely before frosting.
06 - Beat room-temperature butter until smooth and creamy. Gradually add powdered sugar, alternating with whole milk, and blend in vanilla extract. Whip on high speed until frosting is light and fluffy.
07 - Separate the buttercream into three bowls. Tint one portion with red gel color, one with blue, and leave the third white. Fill a piping bag fitted with a large star tip, placing spoonfuls of each color side by side for a swirl effect.
08 - Pipe tall swirls onto cooled cupcakes. Adorn with festive sprinkles and star candies. Insert mini sparklers or themed toppers just prior to serving and remove before consumption.