Preheat oven to 350℉ / 175℃. Line a baking sheet with parchment paper.
In a medium bowl, mix the peanut butter, turbinado sugar, and egg whites with a spoon until smooth. The dough will be quite soft.
Divide the dough into two portions. Add the cocoa into one of them, so you have chocolate and a peanut butter doughs.
Scoop the cookie dough using a #40 (1 1/2-tablespoons) portion scoop, by filling half with the peanut butter and half with the chocolate dough. Place the dough balls evenly, about 2 inches apart, on the prepared baking sheet.
Freeze for 15 minutes or until the dough balls are stiff.
Roll the frozen dough balls between the palms of your hands into round spheres. Dip into turbinado or Crystal decorating sugar. Use a fork to creat cross-hatch marks and flatten to disks 1/2 inch / 1.3cm thick. You can make the cookies larger or smaller, but it will affect the baking time.
Bake in the middle of the oven for 10 to 12 minutes, until golden brown along the bottom and set on top.
Cool completely on the baking sheet, then dunk in milk or eat however you please.