Preheat oven to 300°F. Line baking pan with parchment paper or silicone liner or use greased muffin top pan.
Separate the eggs into separate bowl.
Add the mascarpone cheese, stevia, and salt to the yolks. Blend well with an electric mixer.
Sprinkle cream of tartar on the egg whites if desired. Whip with a clean electric mixer until very stiff.
Using a spatula, gradually fold the egg yolk mixture into the white mixture. Try not to break down the egg white, you want it to stay fluffy.
Spoon 4 mounds of the mixture onto the prepared baking pan or molds. Flatten each mound slightly.
Bake for about 25-30 minutes. Do not over bake or they can become crumbly.
Cool on the baking pan for 3-5 minutes, then transfer to a cooling rack.
Allow the cakes to dry on rack for the day.
Whip all frosting ingredients together until fluffy.
Frost the top of each cake layer, stacking on top of each other.
