1. Preheat the oven to 350°F and line a 12-cup muffin pan with cupcake liners.

2. In a medium bowl, whisk together the flour, baking powder, and salt.

3. In a large bowl, beat the softened butter, peanut butter, granulated sugar, and brown sugar until smooth and fluffy.

4. Beat in the eggs one at a time, then mix in the vanilla extract.

5. Add the dry ingredients in two additions, alternating with the milk, and mix just until combined.

6. Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

7. Bake for 18 to 21 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

8. Cool the cupcakes in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

9. For the frosting, beat the butter and peanut butter until smooth and creamy.

10. Add powdered sugar, heavy cream, vanilla extract, and salt, then beat until fluffy and pipeable.

11. Pipe the frosting over the cooled cupcakes and top each one with chopped or halved mini peanut butter cups.