Preheat the Oven:
Preheat your oven to 350°F (175°C). Lightly grease a mini muffin pan or line with paper liners.

Make the Dough:
In a large mixing bowl, cream together softened butter, peanut butter, granulated sugar, and brown sugar until smooth and fluffy.
Beat in the egg and vanilla extract until fully combined.

Add Dry Ingredients:
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually mix the dry ingredients into the wet ingredients until a soft dough forms.

Shape and Fill:
Roll dough into 1-inch balls (about 1 tablespoon each) and place one ball in each cup of the mini muffin pan.

Bake:
Bake for 8–10 minutes, or until the tops are lightly golden and set. Immediately after removing from the oven, gently press one mini peanut butter cup into the center of each cookie.

Cool:
Let the cookies cool in the pan for 10–15 minutes before transferring to a wire rack to cool completely.