In a large mixing bowl, cream butter and peanut butter. Add sugar, brown sugar, egg and vanilla; mix well. Stir together flour and baking soda; gradually add to butter mixture, beating until well blended. Shape dough into 48 balls (1-inch each); place balls in bottom of ungreased mini muffin cups. Bake at 350° for 8-10 minutes or until lightly browned. Remove from oven. Immedaitely press a peanut butter cup onto center of each. Let cool completely. Remove from pans.