PREHEAT THE OVEN AND PREPARE THE PAN: Preheat your oven to 350°F (175°C). Grease and line a 9x13-inch baking pan with parchment paper to prevent sticking.
MIX DRY INGREDIENTS: In a medium bowl, whisk together the flour, baking powder, and salt until evenly combined. Set aside.
CREAM BUTTER AND SUGAR: In a large mixing bowl, beat the butter and sugar together on medium speed until light and fluffy, about 3 minutes. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
ADD FLOUR AND MILK: Alternately add the dry mixture and milk to the creamed mixture, starting and ending with the dry ingredients. Mix just until incorporated to avoid overmixing.
COLOR THE BATTER: Divide the batter evenly into three bowls. Leave one portion plain. Color the second portion with red gel food coloring and the third with blue gel food coloring, using enough to create bold colors that stay vibrant after baking.
SWIRL INTO PAN: Drop spoonfuls of each colored batter into the prepared pan, alternating colors to create a scattered pattern. Lightly swirl through the batter with a toothpick or knife to create a marbled effect. Do not overmix.
BAKE THE CAKE: Bake for 28 to 32 minutes or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.
CRUMBLE THE CAKE: Once cooled, crumble the cake into a large bowl using your hands or a fork. Gently break it up without overmixing so the red, white, and blue swirls remain visible.
MIX WITH FROSTING: Add about ¾ cup of the prepared frosting and mix by hand until the mixture holds together like dough. Add more frosting in small amounts only if needed for binding.
ROLL INTO BALLS: Use a tablespoon or cookie scoop to portion the mixture, then roll into tight balls about 1.5 inches in diameter. Place them on a parchment-lined baking sheet.
CHILL THE CAKE BALLS: Refrigerate the cake balls for 1 hour or freeze for 20 minutes until firm. This helps them hold their shape during dipping.
MELT THE COATING: In a microwave-safe bowl, melt the white chocolate or candy melts in 30-second intervals, stirring between each. Add vegetable shortening or coconut oil to achieve a smooth, pourable consistency.
INSERT STICKS: Dip the tip of each lollipop stick into the melted chocolate, then push it halfway into each cake ball. This step helps secure the stick in place.
DIP THE CAKE POPS: Dip each cake pop into the melted chocolate, turning to coat completely. Let the excess drip off and place the pops upright in a stand or foam block.
DECORATE IMMEDIATELY: While the coating is still wet, sprinkle with red, white, and blue star-shaped sprinkles. Allow the coating to set completely before serving.