In a mixing bowl, stir together the flour, salt and baking soda; set aside.
In a separate mixing bowl, cream together the butter, sugar, peanut butter and brown sugar until fluffy.
Beat in the egg, vanilla and milk with the creamed butters and sugar.
Add in the flour mixture with the wet mixture; mix well.
Shape into 40 balls and place each ball into an ungreased mini muffin pan.
Bake for about 7-8 minutes. Remove from oven and immediately press a mini peanut butter cup into each ball. Let the cookies cool, then carefully remove from pan.
Notes
To remove the cookies take a small knife and just run it on the outside of the cookie to make sure nothing is sticking to the pan. Then take a spoon or fork, and carefully pop them out of their hole, holding it steady with your other hand so the melted chocolate peanut butter cup stays in place.