01 - Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with themed cupcake liners.
02 - Whisk together the flour, baking powder, and salt in a medium bowl.
03 - In a large bowl, beat unsalted butter and granulated sugar until light and fluffy using an electric mixer.
04 - Add eggs one at a time, mixing thoroughly after each addition, then blend in vanilla extract.
05 - Add flour mixture in three batches, alternating with milk, beginning and ending with flour. Mix until just combined.
06 - Evenly divide the batter among cupcake liners. Bake 18–20 minutes, or until a toothpick inserted in the center comes out clean. Cool completely on a rack.
07 - In a clean bowl, beat softened butter until smooth. Gradually blend in sifted powdered sugar, then add milk and vanilla. Beat until frosting is airy and fluffy.
08 - Divide the frosting into three portions. Tint one red, one blue, leaving the third white. Mix colors thoroughly using gel food coloring.
09 - Fit a piping bag with a large star tip. Spoon alternate colors of frosting into the bag to create a multi-colored swirl. Pipe tall swirls atop cooled cupcakes.
10 - Sprinkle with red, white, and blue decorations and place star-shaped candies or sugar pearls. Insert sparklers or decorative toppers just before serving; remove these before eating.