Preheat oven to 375F.
Separate the egg whites from the yolks. Add cream of tartar to the whites and whisk until peaks are formed.
In a food processor, combine 1/2 of the beaten egg whites, melted butter, almond flour, yeast, apple cider vinegar, baking powder, salt and erythritol. mix until well incorporated.
Pour in the remaining 1/2 of mixed egg whites and gently process until you get a lumpy thick dough. Important – do not overmix!
Pour dough into a prepared buttered loaf pan. Smooth out the top surface with a spatula. (optional – sprinkle sesame seeds on top)
Place in oven and bake for 30 minutes.
Bring the oven-baked bread out of the oven and let it cool for about 20 minutes.
Slice and serve.