Preheat oven to 375 degrees F (190 degrees C). Sift together the flour, salt and baking soda, set aside.
Cream together the butter, sugar, peanut butter and brown sugar until fluffy. Beat into the egg, vanilla and milk. Add to flour mixture, mix well.
Shape into 40 balls and place each into an ungreased mini muffin pan. Bake at 375 degrees F for about 8 minutes.
Remove from oven and immediately press a mini peanut butter cup into each ball. Cool and carefully remove from pan.
Ingredients: