In small bowl, mix flour, cocoa, baking soda, cocoa and black pepper. Set aside.
In large bowl, beat softened butter and sugars with electric mixer on medium speed, or mix with spoon about 1 minute or until fluffy, scraping side of bowl occasionally.
Beat in egg, mint and vanilla until smooth.
Stir in flour mixture just until blended (dough will be stiff). Stir in chocolate chips.
Form into balls and lay on a flexible cutting board. Freeze until firm but before ice crystals form, about 20 minutes.
Baking
When ready to bake, heat the oven to 375 °F (191 °C), put the cookies on an ungreased or parchment-lined cookie sheets. Although the cookies will not spread very much, put only 12 spaced apart by 2 inches.
Bake 8 to 10 minutes or until light browned (centers will be soft). Cool 2 minutes; remove from cookie sheet to cooling rack.
Rolling
When the cookies are cool enough to handle, roll them in powdered sugar.
Cool completely, about 30 minutes.
Coating
Mix the sanding sugar and mint in the food processor until the sugar is very fine. Mix with 1/2 cup powdered sugar. Set Aside.
Roll the cookies in the mint flavored powdered sugar.
Store covered in airtight container.
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