Preheat oven to 325 degrees F. In a large bowl, whisk together flour, sugar, cocoa powder, and salt.

Add butter, peanut butter, and vanilla. Use a pastry blender to incorporate. Form the dough into a ball and knead until smooth.

Roll dough to 1/3-inch thick on a floured surface. Cut out cookies and place on an ungreased cookie sheet.

Bake for 15-20 minutes or until centers are set. Cool on sheets for 5 minutes, then transfer to a wire rack.

For icing, microwave chocolate chips with half shortening in intervals, stirring until melted. Repeat with peanut butter chips and remaining shortening.

Spread half of the cookies with chocolate icing and the other half with peanut butter icing. Drizzle with leftover icing.

Store in an airtight container. Can be frozen for up to three months.