Preheat the oven to 350 F. Place the cupcake liners in the muffin pan.

In a small bowl, combine the flour, baking powder, and salt. Set aside.

In a medium bowl, whisk together the butter and sugar. Add the egg and vanilla and whisk until combined.

Add half of the flour mixture to the butter mixture and whisk until combined. Add the milk and the second half of the flour mixture. Whisk until smooth.

Separate the batter into two bowls. Add a couple drops of pink gel food coloring to one bowl and stir until well combined. Add a couple drops of purple gel food coloring to the other bowl and stir until well combined.

Transfer the batter to the prepared muffin pan by spooning in alternating colors of batter into each muffin cup.

Bake for 15 minutes or until a toothpick inserted in the center comes out clean. Let cool completely before frosting.

In a medium bowl, beat the butter and vanilla until smooth.

Add the sugar and the milk. Beat until combined.

Beat the frosting on high speed until fluffy.

Separate the frosting until two bowls. Add a couple drops of pink gel food coloring to one bowl and stir until well combined. Add a couple drops of purple gel food coloring to the other bowl and stir until well combined.

Transfer the frosting to the two smaller piping bags. Place the large star tip into the large piping bag. Cut off the tips of the smaller piping bags and place them into the larger piping bag.

Press firmly on the larger piping bag so that both colors of frosting come out of the tip at the same time. Frost the cupcakes by piping the frosting in a swirl around the top of each cupcake.