Preheat oven to 350°.
Cream together the butter, granulated sugar and brown sugar.
Add the egg and vanilla. Mix until light in color and creamy.
Add in the dry ingredients (flour, cocoa, baking soda and salt), mix into the dough. Mix until completely combined. The dough will be soft.
Fold in the peanut butter chips.
Scoop ½ cup of cookie dough out and roll into a ball and then flatten slightly. Arrange 6 on each cookie sheet. Add extra peanut butter chips to the top if desired.
Bake at 350° for 12-15 minutes or until the cookies have spread slightly, are puffy and no longer glossy on top.
Allow the cookies to cool for 15 minutes on the pan. Serve warm.
