Preheat oven to 350 degrees F and generously grease a 6 cavity donut pan.
In a large mixing bowl, combine the almond flour, coconut flour, tapioca flour, baking soda and salt.
In a separate bowl, whisk together the eggs, apple cider vinegar, coconut oil, vanilla, coconut sugar, and milk.
Make a well in the flour mixture and then pour in liquid ingredients. Mix until all ingredients are fully incorporated. The batter will be thick.
Transfer donut batter into a piping bag, or plastic sandwich bag. Cut the tip/corner of the bag about ½" - ¾". Pipe batter into donut pan, filling each cavity about ¾ of the way full.
Bake for 15-17 minutes, or until golden brown and they start to pull away from the edges (see notes).
Allow donuts to cool slightly before removing them from the pan. If using silicon, you can flip the pan over and loosen the donuts by very carefully pushing on the silicone. Transfer donuts to a wire cooling rack and allow to fully cool before adding the chocolate frosting.
While donuts are cooling, make the chocolate frosting. In a small shallow bowl, whisk together the powdered coconut sugar, cocao, and milk (or water). You want the bowl shallow enough that you can dip the donuts in it.
Once donuts have cooled, carefully dip each donut in the frosting. Dip the top half of each donut (on the rounded side) into the chocolate frosting. The frosting will be thick, so be careful when dipping and pulling the donut out. Place donut back on cooling rack to let frosting settle.
Enjoy!