Mix cashew butter, water, and stevia until combined. Start with only 2 tablespoons of water.
Add protein powders and cocoa, and mix to combine. You may need to use your hands. And if you need more water, add by the teaspoon.
Roll or press the dough to flatten (easier to roll between sheets of parchment paper).
Use a cookie cutter to cut 12 circles, and lay them on a parchment-lined cookie sheet.
Bake for about 12 minutes, or until firm.
Remove from oven and let cool.
Mix confectioners erythritol with water.
Turn 6 cookies over, and spread with icing. Top with additional cookies. Enjoy!
Notes
A note about substitutions: You could use all vegan or all whey protein in these cookies (for most whey powders). If you go with all whey, start with only 1 tablespoon of water.