Preheat the oven to 350°F (175°C).

In a mixing bowl, cream together the softened butter, creamy peanut butter, brown sugar, and granulated sugar until smooth.

Add the egg and vanilla extract, and mix until well combined.

In a separate bowl, whisk together the flour, baking soda, and salt.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Fold in the chopped Reese's Peanut Butter Cups and Reese's Pieces.

Drop tablespoon-sized balls of dough onto a baking sheet lined with parchment paper.

Bake for 10-12 minutes or until the edges are golden brown.

Allow cookies to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.