Preheat oven to 375 and grease a mini muffin tin.
Unwrap about 40 miniature peanut butter cups and store them in the fridge until the cookies are done.
Cream the butter and sugars together with a mixer.
Mix in the egg and vanilla.
Add in the peanut butter and milk.
Add the dry ingredients: flour, salt, and baking powder.
Mix until combined.
Spoon about 1/2 tbsp. of dough into each muffin cup.
Bake for 9 minutes or until the top starts to brown.
As soon as the cookies come out of the oven, gently place a peanut butter up into each muffin cup.
Let cool completely before trying to remove from the pan.