Preheat oven to 325F (163C).
Combine all the dry ingredients: protein powder, cacao, coconut flour, baking powder, salt, erythritol.
Mix in the coconut oil and almond-coconut milk. You may need to use your hands to be sure the dough is well combined.
Roll the dough on parchment paper, and cut 20 circular cookies using a cookie cutter. Or, roll the dough into 20 balls, and flatten each in your hand.
Place cookies on a parchment-lined baking sheet, and bake for 10-12 minutes until firm.
Remove cookies from oven, and let cool.
Meanwhile, place frosting ingredients in a blender or food processor. Process until smooth.
Make cookie sandwiches by spooning frosting between two cookies.
Enjoy! Store extras in the refrigerator.