By definition, a sponge cake is a light. Airy tender cake of the foam variety, meaning the egg whites are beaten separately, and the egg yolk base is folded into the whites along with flour. It can be varied easily and is used as a base for many fillings. The name comes from its open structure, which resembles a sponge. The plain sponge cake on its own is rather neutral and doesn't have a lot of flavor which is why recipes often brush the sponge cake layers with liqueur based washes.. However, by enhancing it with lemon zest and adding a little butter, it becomes a more flavorful vehicle for fillings. By omitting the zest, you have a basic Butter Sponge Cake. By omitting the butter, you have a basic Sponge Cake.
Another characteristic of the sponge is that it doesn't contain shortening, except in the Butter Sponge Cakes. Sponge cakes can be dry if the egg whites are over beaten. It is better to under beat them than get them too stiff. When the whites are too stiff, it is difficult to fold the flour in without deflating the whites.
Normally, any type of sponge cake or Genoise, the French version, are leavened only with the beaten whites and the air beaten into the yolks. I have added baking powder to insure success, especially if you are new to this type of cake. It can certainly be omitted if you are a purist.
It is important to beat the egg yolks with the sugar and vanilla until light and almost white in color. The whites are beaten with a bit of sugar to stabilize them, and the two are folded together with flour. To make it is easier to incorporate the flour, half is added at a time and the flour is sifted into the mixture to lighten it.
The butter can be difficult to incorporate if added directly to the sponge cake batter as it has a tendency to sink to the bottom of the bowl. By taking a small amount of the batter and whisking in the melted butter, the mixture is emulsified and much easier to fold into the larger amount of batter.
Sponge cakes have a well deserved reputation for being difficult. However, by following the steps below and being careful not to over beat the egg whites, it really is easy to bake the perfect Lemon Butter Sponge Cake.
This recipe makes three layers, about 1 ¼ inches each. At the end, I give you the ingredients for a two layer version.
This cake will be used in a follow up blog at a later date for one of Vienna's most famous cakes – the Dobos Torte.
Lemon Butter Sponge Cake
1 ¼ cups cake flour (150 grams or 5 ⅓ ounces)
1 ½ teaspoon baking powder
9 eggs, separated
1 cup sugar, divided (200 grams or 7 ounces)
1 ½ teaspoons vanilla
2 lemons, zested
6 tablespoons butter, melted
Preheat the oven to 350 degrees. Line three 9x2 inch cake pans with parchment rounds and spray the centers only. See Cake Pan Prep Set aside.
Whisk together the flour and baking powder and set aside.
Place the egg yolks, ½ cup of sugar (100 grams or 3 ½ ounces) and vanilla in a mixing bowl fitted with the whisk attachment. Beat until very pale yellow and very fluffy. Towards the end, add the lemon zest. The mixture should form ribbons when the whisk is lifted.
In a clean bowl with a clean whisk attachment, place the egg whites. Beat until the whisk leaves a trail in the egg whites. Slowly add the remaining sugar and beat to medium peaks. Pour the egg yolk mixture and sift half the flour over the egg whites. Very gently, fold in. Sift the remaining flour over the batter and fold together. Take about 1 cup of batter and remove to a bowl. Whisk in the butter; return this to the main amount of batter and whisk in. Divide between the three pans (290 grams or 10 ounces each) and smooth tops using a small offset spatula... Bake for 12 to 14 minutes. They will just begin to color and spring back when the center is lightly touched. The layers will be flat and still clinging to the side of the pans.
Cool completely. To release the sponge cake layers, go around the edges with a small, flexible spatula. Turn the layer out, remove the parchment and turn right side up. See Cake Pan Prep.
At this point, they can be used immediately or frozen. I freeze the layers individually without covering them, as they are tender and easily squashed at this point. As soon as they are frozen, I cover them for longer storage.
Yield: 870 grams or 30 ounces. Three layers about 1 ⅛ each each.
Two Layer Ingredients
1 cup sifted cake flour (100 grams or 3 ½ ounces)
1 teaspoon baking powder
6 egg, separated
¾ cup sugar, divided (150 grams or 5 ⅓ ounces)
1 teaspoon vanilla
1 large lemon, zested
4 tablespoon butter, melted (60 grams, 2 ounces or ½ stick)
Follow the directions above.