In a separate bowl, whip the egg whites until stiff. Gently fold them into the cake batter by hand using a wooden spoon or spatula. Again, you don't want to over-mix the batter.
4 eggs, separated
Pour one layer (1/4 cup) of batter into a greased ring tin. Bake the layer for 3-4 minutes and remove when it is golden brown.
Remove the tin from the oven and add another layer and repeat the process until all layers are baked. Depending on the size of your pan and the thickness of the layers you'll end up with about 8-10 layers.
Once baked, let the cake completely cool.
To make the chocolate glaze, break the chocolate into small pieces and put it in a small bowl along with the butter. Using the double boiling method, place the bowl over simmering water, making sure it doesn't touch the water. Melt the chocolate and butter while stirring constantly. Remove the glaze from the heat and add it to the Baumkuchen straight away. You can have a smooth glaze or create a bark-like pattern using a brush or fork.
100 g dark chocolate, 1 tbsp butter
Notes
Room temperature: Set the butter and the eggs out about 30 minutes before to baking. This will allow the ingredients to mix well together. Room-temperature eggs also help the cake rise properly.Don’t over-mix: You'll want to make sure you don't over-mix the batter. Over-mixing adds air into the batter, this can cause the cake to not back properly or evenly. You will also want to make sure you fold the egg whites gently.Cool completely: As tempting as it may be, you need to make sure the cake is completely cooled before adding the glaze. If it's too hot, the glaze won't stick and set.