1. Preheat the oven to 350°F (175°C) and line a muffin pan with cupcake liners.

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

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

4. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

5. Mix in the sour cream until fully combined.

6. Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Mix until just combined.

7. Fill the cupcake liners about two-thirds full with batter.

8. Bake for 18 to 22 minutes or until a toothpick inserted into the center comes out clean.

9. Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

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

11. Gradually add the powdered sugar, then mix in the heavy cream and vanilla extract until fluffy.

12. Pipe the frosting onto the cooled cupcakes.

13. Top each cupcake with half of a mini peanut butter cup.

14. Serve immediately or store in an airtight container.