01 - Preheat oven to 350°F. Line a 12-cup muffin tin with festive cupcake liners.
02 - In a mixing bowl, whisk together all-purpose flour, baking powder, and salt until evenly blended.
03 - Using an electric mixer, beat unsalted butter and granulated sugar together until light and fluffy. Add eggs one at a time, mixing well after each addition. Incorporate vanilla extract.
04 - Add the flour mixture in thirds to the butter mixture, alternating with whole milk. Begin and end with the flour, mixing just until combined. Do not overmix.
05 - Evenly divide batter among prepared cupcake liners. Bake for 18 to 20 minutes, or until a toothpick inserted into the center comes out clean. Allow cupcakes to cool completely on a wire rack.
06 - In a clean bowl, beat unsalted butter until creamy. Gradually add sifted powdered sugar, then whole milk and vanilla extract. Beat on high speed until frosting is light and fluffy.
07 - Split frosting evenly into three bowls. Tint one portion with red gel food coloring, one portion with blue, and leave the remaining white.
08 - Fill a piping bag fitted with a large star tip with spoonfuls of each colored buttercream to create a swirl effect. Pipe tall swirls onto cooled cupcakes.
09 - Garnish frosted cupcakes with red, white, and blue sprinkles and star-shaped candies or sugar pearls as desired. Insert mini sparklers or themed toppers before serving; remove non-edible decorations before eating.