Preheat the oven to 350°F / 175°C. 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.
Scoop the cookie dough using a #40 (1½-tablespoon) portion scoop and place evenly, about 2 inches apart, on the prepared baking sheet, then flatten to disks ½ inch / 1.3cm thick. You can make the cookies larger or smaller, but it will affect the baking time. Sprinkle with the sugar (if using).
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.
