What is a sponge cake?
A sponge cake is the basis of any Torte (layered cake) so it needs to be perfect every time. In Germany, this type of base is called Biskuitmasse/Biskuitteig/Biskuitboden or, simply, Biskuit, and consists of eggs, sugar, and flour which is sometimes mixed with starch to get a lighter cake flour. For the dark sponge cake, Dutch-process cocoa is added. Some versions also add some fat (melted butter or vegetable oil).
The ratio for a basic sponge cake:
1 egg (60 g) <=> 30 g caster sugar + 30 g all-purpose flour
What is the difference between Biskuit (sponge cake), Genoise and Wiener Boden?
For Biskuit the egg whites are usually beaten separately.
Genoise and Wiener Boden/Masse are 2 other types of sponge cake where the eggs are not separated, but beaten together with sugar on a water bath. The last one also has fat added, either melted butter or vegetable oil.
Adding fat (butter, oil) to the batter helps create a moist cake that will also hold longer.
For making the Genoise or Wiener version, you beat the whole eggs with sugar and salt for few minutes on a water bath until it reaches the finger temperature and the sugar melts (no more than 40°C ). Remove batter from the heat and beat it thoroughly until it becomes light and fluffy and considerably increased its volume. Gently incorporate the sifted flour.
For Wiener version, you can now add melted butter or vegetable oil (I usually use 35 g melted cold butter or 25-30 ml. vegetable oil for a Ø 26 cm cake pan). You can also add flavoring to your liking (vanilla is my first choice). To be baked as described above. This version is easier to make if you have a stand mixer do the work for you. With a hand mixer/whisk, it will take slightly longer until you get the fluffy texture.
Check out my detailed recipe with step by step instructions for a basic fluffy sponge cake which can be reduced to 3 main ingredients, which is perfect for people with lactose intolerance.
My recipe with fat and flavors for a slightly moist layer cake basis: German Sponge Cake (Biskuit).