Beat butter, sugar and peanut butter in large bowl until well blended. Add egg and vanilla; beat well. Stir together flour, baking soda and salt; add to butter mixture, blending well. Stir in mini peanut butter cups. Drop by heaping teaspoons onto UN greased cookie sheet.
Bake 12 to 14 minutes or until light golden brown around the edges. Cool 1 minute; remove from cookie sheet to wire rack. Cool completely. About 2-1/2 dozen cookies