This recipe makes one tall 9 inch inch cake. If using 8 inch cake pan line the sides of the pan as cake will be little taller than 9 inch cake. You can double this recipe to make 10 inch cake. Be sure to use heating core if using 10 inch cake pan.
Preheat oven 350F. Butter and flour your baking pan, line the bottom with parchment. Or use nonstick spray and line the bottom with parchment.
In a large bowl whisk together flour (1 and 1/2cup), salt (1/4tsp) and baking powder (1tsp), set aside.
In a clean bowl, whip egg whites ( 4 egg whites) with a pinch of cream of tartar or 1/2tsp lemon juice/white distilled vinegar(optional). Beat until foamy. Then gradually add 1/2 of the granulated sugar (1/2cup). Beat until stiff, shiny and moist peaks are formed. Don't over beat of meringue will be dry.
Gently scrape the meringue into another bowl. Set aside. Now we are going to prepare egg yolk mixture, no need to clean the mixer bowl.
Place egg yolks (4 egg yolks) into the mixing bowl you just used for making the meringue. It is okay, it doesn't have to be spotless. Add remaining granulated sugar (1/2cup) to the egg yolks. Beat using wire whip attachment. Beat the egg yolks at medium-high speed. Scrapping the bowl once or twice to ensure all egg yolks are well blended in. Beat until ribbon stage is reached. About 5-6 ,minutes. Mixture will be thick, doubled in volume and pale in color.
Gradually in one continuous pour add oil, mix well. The gradually add warm water. Scrape the bowl in between. Beat in vanilla extract and beat for 2 more minutes. Turn off the mixer.
Using fine mesh strainer sift about 1/3 of flour mixture into the egg yolk mixture and carefully fold the flour in with a spatula, then add about 1/3 of meringue and fold in. Continue with the rest of the flour and meringue until no streaks are visible. Then make last 3 folds, making sure you go with the spatula all the way to the bottom of the bowl. Be gentle and don't over mix. You are looking for a light and airy batter.
Fill your prepare baking pan and bake until tooth pick inserted in the center comes out clean, about 25-30 minutes. 10 inch can take up to 35 minutes to bake.
Let the cake cool for 5 minutes in the pan. Invert it on a cooling rack and let cool completely. Wrap the in a food safe plastic wrap.
Store undecorated/unfilled cake covered in the fridge for up to 5 days until ready to use. Or fill the cake with your favorite frosting. Store in the fridge for 5 days. If using whipped cream make sure to use some gelatin to stabilize it so whipped cream doesn't weep.
Stored in the fridge, covered, in a container or bakery box cake lasts for 5 – 6 days. You can keep unfilled sponge cake at room temperature for 2-3 days.
Freeze sponge cake right after it cools, tightly and well wrapped in a food plastic wrap. I prefer freezing it without the filling. You can freeze a sponge cake for up to 3 months. Let it thaw on the counter.
Sugar crystals were not completely dissolved. Also under-mixing can be an issue. Stirring instead of folding of the batter at the last stage of mixing.
Check the raising agent expiration date. It can also mean that cake wasn’t baked long enough.
Over-beated egg whites. Over baking. To amend a dry sponge, use simple syrup.
This is usually caused by over-mixing. Quick solution, fill the holes with buttercream.
There are number of icing/frosting that work well with a sponge cake. My personal favorites are: Whipped Cream, German Buttercream, Lemon or Raspberry Curd, jam or any fruit filling such as Strawberry Mouse.