Preheat oven to 350F. Whip egg whites until they have stiff peaks (this is the most important part and will ensure you get a great fluffy consistency).

Combine the egg yolks, sweetener, vanilla, and butter in a separate bowl, then whisk until well mixed.

Combine almond meal, salt, baking powder, cinnamon, and cocoa powder in a third mixing bowl.

Gently (really gently) fold the wet ingredients into the whipped egg whites.

Slowly add the bowl of mixed dry ingredients to the wet mixture while continuing to mix.

Fill the donut pan ¾ of the way full on each mold.

Bake for 15 minutes, or until a toothpick comes out clean. In a separate bowl, combine casein powder and heavy cream until it is thick and forms the icing.

Pour the icing over the donuts when they have cooled down a bit.