Preheat your oven to 375 degrees F and spray your muffin tin with cooking spray.
Beat together the butter, peanut butter, and sugars.
Add in the vanilla, milk, and eggs, and beat again.
Stir in the flour, baking soda, and salt.
Once the dough is formed, use a cookie scoop to scoop out your dough, roll it into a ball, and then roll it in a bowl with the ‘topping’ sugar until all balls are coated with sugar.
Place each ball into your muffin tin and gently press them down into the muffin tin with the back of a measuring spoon and bake for 10-12 minutes or until slightly golden.
While the cookies are baking, unwrap the mini peanut butter cups.
As soon as you remove the cookies from the oven, place a mini peanut butter cup into each one, pressing down gently.
Allow to cool and enjoy!