Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.
In a bowl, whisk together flour, baking powder, and salt.
In a separate bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, then vanilla.
Alternately mix in the flour mixture and milk, beginning and ending with flour. Mix just until combined.
Divide batter evenly among cupcake liners. Bake for 18–20 minutes or until a toothpick comes out clean.
Let cupcakes cool completely. Then, using a small knife or cupcake corer, cut out a 1-inch hole in the center of each cupcake.
Fill each center with about 1 tablespoon of mini candies.
Replace the cut-out piece on top to cover the filling.
Make the frosting: Beat butter until creamy. Add powdered sugar gradually, then vanilla, salt, and milk until desired consistency.
Frost cupcakes and decorate with sprinkles or additional candy as desired.