Preheat oven to 375 degrees Fahrenheit. In a mixing bowl cream together the butter, shortening, peanut butter, granulated sugar, and brown sugar until light and fluffy, 1 to 2 minutes. Add eggs, mixing after each addition. Mix in the vanilla.

In a separate bowl whisk together flour, baking soda, and salt. Stir dry ingredients into the wet ingredients and mix gently to combine. (Don't overmix!--The dough will be very soft).

Pour ¼ cup of granulated sugar into a bowl. Roll dough into ½ inch size balls and then roll in sugar. Place on an ungreased cookie sheet and bake for 6 to 8 minutes, until set, but not browned. You really don't want to over-bake the cookies or they will be hard. Remove from oven and allow the cookies to rest on baking sheet for 2 to 3 minutes, then transfer the cookies to a cooling rack.

For the frosting: Put the butter, cocoa, and milk in a saucepan and bring to a boil. Remove from heat and mix in the powdered sugar and vanilla; beat well until smooth.

Pipe or spread some frosting between two cookies. Repeat. Enjoy!