Stir together flour, cocoa, baking soda and salt. Beat butter and sugar in a large bowl with mixer until fluffy. Add eggs and vanilla; beat well. Gradually add flour mixture, beating well. Stir in peanut butter chips.
Drop by rounded teaspoons onto ungreased cookie sheet. Bake 8 to 9 minutes. (Do not overbake; cookies will be soft. They will puff while baking and flatten while cooling.) Cool slightly; remove from cookie sheet to wire rack. Cool completely. About 4 1/2 dozen cookies.
PAN RECIPE: Spread butter in greased 15-1/2 x 10-1/2 inch jelly roll pan. Bake at 350°F 20 minutes or until set. Cool completely in pan on wire rack; cut into bars. About 4 dozen bars.