Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a bowl, whisk together the flour, baking powder, and salt.
In another bowl, beat the butter and sugar until light and fluffy. Add the eggs one at a time, then mix in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Mix until just combined.
Divide the batter evenly among the cupcake liners and bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let cool completely.
Once cooled, use a small knife to cut a circle in the center of each cupcake and remove a small piece of cake. Fill the hole with the colored buttercream frosting and replace the piece of cake.
Frost the top of each cupcake with the white buttercream frosting.