Preheat the oven to 375 degrees.First, you are going to cream together the butter, peanut butter, sugar, and brown sugar.Then beat in the eggs and vanilla extract.Lastly, mix in the flour, baking soda, and salt.Take a small scoop of the batter and roll into a ball. Place in the mini muffin tin and bake for 8 to 10 minutes. You want to take them out of the oven when they are golden brown.When they are baked, remove them from the oven and press the Reese's Peanut Butter Cups into the center of the cookies.Let the cookies cool for about 5 minutes then remove the cookies from the pan let them finish cooling on a wire rack.Store the cookies in an airtight container. They are best fresh but will last a week or two if stored properly. They also freeze well.This recipe makes about 4 dozen cookies.