Mix the apple cider vinegar, egg, butter, and coconut sugar together in a bowl.
In a separate bowl, mix the almond flour, cocoa powder, baking soda, and salt until no clumps are left.
Combine the wet and dry ingredients gently.
Fold in chocolate chips (optional).
Cover and freeze the dough for 30 minutes or refrigerate overnight.
Scoop the dough into cookie dough balls and roll in tapioca flour then confectioner sugar.
Place them on a parchment-paper-lined baking sheet. The cookies will expand a lot, so leave them in a ball shape and have plenty of room in between each cookie ball.
Bake at 350F for 9 - 10 minutes. If the confectioner sugar on top melts away, dust a generous amount on top of the cookies.