Beat egg white till frothy then rain in the sugar and cream of tar tar. Add the stevia. The total time for beating the egg white to get to the stiff peak is 4 minutes on the Kitchenaid at #6.
Fold the egg whites into the egg yolk mixture, 1/3 at a time.
Bake at 160C for 1 hour, placing the cake on a rack, with another tray of water below the rack. If you don't want the cake to crack, try covering the top of the cake and remove after the first 45 minutes of baking.
Once cooked, take the cake out and turn it upside down.
Unmold by cutting close to the pan using a sharp knife.