1. Heat oven to 350°F. Remove wrappers from peanut butter cups. Cut each cup into approximately 12 pieces; set aside.
2. Beat butter and sugar in large bowl until fluffy. Add peanut butter, beating until smooth. Add egg and vanilla; beat well. Stir together flour, baking soda and salt; add to butter mixture, blending well. Gently stir peanut butter cup pieces into batter. Drop by teaspoons onto ungreased cookie sheet.
3. Bake 10 to 12 minutes or until edges are lightly browned. Cool slightly; remove from cookie sheet to wire rack. Cool completely. About 3 dozen cookies.