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 butter, peanut butter, and granulated sugar until light and fluffy.

4. Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.

5. Add the dry ingredients in batches, 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 22 minutes, or until a toothpick inserted into the center comes out clean.

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

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

10. Gradually mix in the powdered sugar, then add the heavy cream, vanilla extract, and pinch of salt until the frosting is fluffy and pipeable.

11. Frost the cooled cupcakes with the peanut butter frosting.

12. Top each cupcake with a mini peanut butter cup and serve.