Preheat oven to 350°F. Spray a 12-cavity muffin pan with nonstick cooking spray (this may make up to 14 cookies so you may need two pans).

Cream butter, peanut butter, and both sugars in the bowl of an electric mixer fitted with the paddle attachment. Add egg, vanilla, milk, salt, and baking soda. Mix until combined. Slowly add flour and mix until dough comes together. Add 20 of the Reese’s miniatures and use the stand mixer to mix/chop them into the dough. If you’re using a hand mixer for the cookie dough you should chop them slightly before adding them. The stand mixer will chop them for you.

Scoop 2 tablespoon sized balls of dough and press each into the bottom of 12 muffin pan cavities. Press an Oreo on top, then cover with 2 more tablespoons of dough. Sprinkle with remaining chopped miniature peanut butter cups. Add another pan as needed for an extra 1-2 cookies.

Bake for 12-15 minutes, until they just begin to brown. Cool completely and use a knife to help remove them from the muffin pan.

Store in an airtight container for up to 3 days. They can be frozen in sealable containers or ziploc bags between layers of paper towels for up to one month.