Preheat the oven to 350 degrees Fahrenheit and line 2 muffin tins with cupcake liners.

In a large mixing bowl, whisk together the flour, baking powder, baking soda and salt.  Set aside.

In a separate mixing bowl, whisk together the creamy peanut butter, brown sugar, egg, sour cream, milk and vanilla extract.

Create a well in the flour mixture and pour the wet ingredients into the dry ingredients.  Stir until combined.

Pour the batter into the cupcake liners filling them up approximately 2/3 of the way full.

Bake for 20-23 minutes until a toothpick inserted into the center of the cupcakes comes out clean.

Cool the cupcakes completely on a wire rack before topping with the frosting.

In a medium bowl, cream together butter and peanut butter until smooth and fluffy with a hand held or stand up mixer.

Gradually add powdered sugar, alternating with milk, beating after each additional until desired consistency.

Pipe the frosting on to the cooled cupcakes, top with a piece of the peanut butter cups and then they are ready to serve and enjoy!