01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with themed cupcake liners.
02 - In a mixing bowl, whisk together the all-purpose flour, baking powder, and salt until evenly combined.
03 - In a separate large bowl, beat the softened butter with granulated sugar until pale and fluffy using an electric mixer. Add eggs individually, beating well after each addition, then mix in vanilla extract.
04 - Add the dry flour mixture in thirds, alternating with whole milk. Begin and end with the dry mixture. Mix gently after each addition, stopping once the batter is just combined.
05 - Distribute the batter evenly into the prepared liners. Bake for 18 to 20 minutes until a toothpick inserted in the center emerges clean. Allow cupcakes to cool completely before frosting.
06 - Beat room-temperature butter until smooth and creamy. Gradually incorporate sifted powdered sugar, alternating with milk and vanilla, and continue beating on high until the texture becomes light and fluffy.
07 - Divide the buttercream evenly into three bowls. Tint one portion red, another blue, and leave the third white. Using a piping bag fitted with a large star tip, fill with alternating spoonfuls of each color to achieve a swirl effect.
08 - Pipe tall swirls of frosting onto the fully cooled cupcakes. Adorn with red, white, and blue sprinkles and star-shaped candies. For presentation, add sparklers or themed toppers immediately before serving, removing them before eating.