Place the cashews, egg yolks, vinegar, milk, and butter in a food processor, and process until very smooth. Add the coconut flour, almond flour, and salt and process again until a smooth and a sticky dough has formed.
Beat the egg whites in a separate bowl until stiff peaks have formed.
Add the baking soda and egg whites to the food processor, then pulse 8-10 times until everything is incorporated.
Using very wet hands, shape the dough into 4 buns, almost like hamburger patties. Re-wet your hands in between each bun to ensure the dough doesn’t stick to your hands and to achieve a smooth exterior.
Bake on a cookie sheet lined with parchment paper or a SilPat for 25 minutes.
These are best eaten within a day, but can be frozen and toasted for later use.