1. Heat oven to 350 deg. F.
2. Beat butter and sugar in medium bowl until fluffy. Add peanut butter, beating until smooth. Add egg and vanilla; beat well. Stir together flour, baking soda and salt; gradually add to butter mixture, beating until blended (dough will be soft). Roll dough into 1-1/2 inch balls; place about 3 inches apart on ungreased cookie sheet. (Cookies spread while baking.)
3. Bake 13 to 14 minutes or until cookie is set and edges are lightly browned. Cool several minutes; remove from cookie sheet to wire rack. Cool completely.
4. Transfer frosting to pastry bag with basket weave tip. Pipe diagonal stripes of frosting across cookies to resemble the wrappings on a mummy. Place 2 mini peanut butter cups as eyes; pipe additional stripes in opposite direction, partially covering "eyes" so that the eyes seem to be peering from beneath the wrappings. Makes about 20 mummy cookies.