Cream together the butter, peanut butter, sugar, and salt. Add the vanilla, egg, and cocoa powder. Mix well, then switch to dough hook or large spoon and add the flour. Mix until dough is smooth.
Fill cookie press with dough and press onto an unlined baking sheet. Press out the cookies, leaving a little space between each. Bake for 6-7 minutes (dark baking sheet 6 minutes, light colored baking sheet 7 minutes).