1. Heat oven to 350°F. Grease 15-1/2x10-1/2x1-inch jelly-roll pan.
2. Beat butter and sugar in large bowl until light and fluffy. Add eggs and vanilla; beat well. Stir together flour, cocoa, baking soda and salt; gradually blend into butter mixture. Stir in peanut butter chips. (Batter will be stiff.) Spread batter in prepared pan.
3. Bake 20 minutes or until set. Cool completely in pan on wire rack; cut into bars. About 4 dozen bars.