First mix all dry ingredients, then add the egg white, apple cider vinegar and water and mix well. If you don`t have almond or flaxseed flour, you can replace it with neutral protein powder.
Then fill the dough into a greased silicone box form and sprinkle with sunflower seeds. Bake at 170 degrees for around 110 minutes. It is best to put a fireproof bowl with water in the oven, then the crust will be nicer.