Line a sheet tray with parchment paper and set aside for now.
Place the yeast, erythritol and warm water in a mixing bowl, mix and let sit for 10 minutes.
In a separate bowl, mix the almond flour, ground flaxseed, whey protein powder, psyllium husk powder, xanthan gum, baking powder, salt and cream of tartar to the bowl and mix everything together well.
Add the egg, egg white, butter and apple cider vinegar to the yeast mix and stir well. Mix until frothy.
Add the flour mix and the sour cream to the bowl and stir everything together well. The dough will become thick quickly.
Divide the dough into 8 round balls, placing them on the prepared sheet tray. You may want to wet your hands slightly to make the dough easier to handle.
Cover the tray loosely with plastic wrap and let the rolls rise for one hour. They should almost double in size.
Preheat your oven to 350 and, once the rolls have risen, bake for 25 minutes or until golden brown.
Let the burger buns cool completely before slicing and using.