In a medium bowl, whisk together the almond flour, coconut flour, psyllium husk powder, baking powder, and salt. Add the eggs, melted butter, and apple cider vinegar. Stir until a thick, uniform dough forms.
Let the dough rest for 3 minutes so the psyllium husk absorbs the moisture and the dough firms up. Divide the dough into 6 equal portions. Roll each piece into a ball, then flatten it into a thick disc about 3 inches wide and 3/4 inch tall. Keep the edges as smooth as possible for an even shape.
Heat a large non-stick skillet over medium-low heat and lightly grease it with butter. This is key - the heat must be low enough to cook the muffins through without burning the outside.
Place 2 to 3 muffins in the skillet, leaving space between them. Cover the skillet with a lid and cook for 5 to 6 minutes, until the bottoms are golden brown and the tops start to look set around the edges.
Carefully flip each muffin, cover again, and cook for another 4 to 5 minutes until the second side is golden and the center is cooked through. Repeat with the remaining muffins.
Let the english muffins cool for a few minutes. Split them open with a fork by piercing around the edge, just like traditional english muffins, to get those signature nooks and crannies. Toast them and serve with butter, cream cheese, or use as a base for eggs benedict.
