1. Heat oven to 350°F. Lightly grease cookie sheet or line with parchment paper.
2. Beat butter and peanut butter in large bowl on medium speed of electric mixer until creamy. Gradually add granulated sugar and brown sugar, beating until well mixed. Add egg and vanilla; beat until light and fluffy. Stir together flour, baking soda and salt; add to butter mixture, beating until well blended. Stir in chocolate pieces. Drop batter by rounded tablespoons onto prepared cookie sheet.
3. Bake 10 to 12 minutes or until lightly browned. Cool slightly; remove from cookie sheet to wire rack. Cool completely. Makes about 18 cookies.