Heat oven to 350'F. Grease 15.5x10.5x1 inch jelly-roll pan. In large mixer bowl, beat butter and sugar 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. Spread batter into prepared pan. Bake 20 minutes or until set. Cool completely in pan on wire rack; cut into bars. Makes about 4 dozen bars.