In and electric mixer cream butter, brown sugar, sugar and peanut butter on medium speed until light and fluffy. Add eggs and beat until well combined.
In a small bowl combine flour, cocoa powder, baking soda, cream of tarter, baking powder and salt. Slowly add to the creamed mixture until well combined. Add chocolate chips and Reese's mini pieces on slow speed until combined.
Drop batter by rounded tablespoon onto a baking sheet. Bake for 8-10 minutes. Cool for 2 minutes before transferring the cookies to a wire rack.
I like ghirardelli chocolate chips and cocoa powder best.