Preheat your oven to 350°F (175°C). Grease a 24-cup mini muffin tin or line it with paper liners.
In a large bowl, beat the softened butter, peanut butter, granulated sugar, and brown sugar until the mixture is light and creamy (about 2-3 minutes).
Add the egg and vanilla extract, and beat until smooth.
In another bowl, whisk together the flour, baking soda, and salt. Gradually mix the dry ingredients into the wet ingredients, stirring just until combined. Fold in the mini chocolate chips.
Scoop 1 tablespoon of dough into each mini muffin cup. Press the dough gently with your fingers or the back of a spoon.
Bake for 8-10 minutes or until the edges are golden brown and the centers are set.
While the cookie cups are warm, press a mini Reese’s peanut butter cup into the center of each cookie cup.
Allow the cookie cups to cool in the pan for 10 minutes, then transfer them to a wire rack to cool completely.