Really light sponge cake

Welcome Antonia. Both are excellent. With the milk sponge cake though, one can mess it up if flour and milk are not folded properly. My motto is patience. With the genoise, it is way easier to do since there is no folding involved. But as with most genoises, it is extremely light but may benefit from some simple sugar syrup. If you split it in two, i suggest maybe 4-5 tbsp syrup on each layer. But it also depends on what you want to do with it.

Here are the recipes that i mentioned in my prior message.
It is 2 recipes.

Milk Sponge Cake (baking911)

The cake used in a Boston Cream Pie can be a buttery one but traditionally it is a sponge cake -- a hot milk sponge cake to be precise. While most sponge cakes are light and somewhat dry, a sponge cake made with milk, has a softer more tender texture. After baking a milk sponge cake several ways -- sometimes heating the milk, other times not, I've concluded that the milk's temperature does not affect the sponge cake's taste or texture at all. So for convenience, my sponge cake recipe calls for unheated milk.

TIP: Eggs contribute to the airiness of this sponge cake. Therefore, it's essential that the eggs be room temperature in order to whip to their best volume.

1 cup sifted cake flour ( I use ¾ cup all purpose flour plus 2 tbsp cornstarch)
1 teaspoon baking powder
1/8 teaspoon salt
1/3 cup milk
3 tablespoons unflavored vegetable oil
3 large eggs, room temperature
1 egg yolk, room temperature
2/3 cup sugar
1 teaspoon vanilla
powdered sugar for decoration
Adjust rack in lower third of oven and preheat to 350 degrees. Line a 9-inch springform pan with parchment or waxed paper; do not grease. Sift flour, baking powder and salt. In a small bowl add the the milk and oil; do not be concerned that they do not blend together.
In a large mixing bowl, whisk the eggs, yolk and sugar to combine. Using an electric mixer at medium speed, whip the egg mixture until it is light ivory in color and very fluffy, about 6 minutes. Add the vanilla toward the end of whipping. Using a rubber spatula, fold in the flour mixture in two additions. Pour the milk mixture down the side of the mixing bowl. (It will sink to the bottom of the bowl under the batter.) Gently fold until the milk mixture is thoroughly incorporated. Pour the batter into the pan. Bake 25 to 30 minutes or until the cake is golden on top and it springs back when lightly pressed in the center. Remove pan from oven to a wire rack until cool.


BEST, LIGHEST AS AIR AND YET EASIEST GENOISE
9 inch springform

4 eggs, separated, room temperature
Pinch of salt
1/2 cup sugar
1/2 cup all purpose flour + 4 tbsp cornstarch + 1 1/2 tsp baking powder
2 tsp vanilla extract

The secret in making this genoise ultra light despite not preparing the eggs « au bain marie » and not folding flour into egg mixture, is in using an electrical mixer and doing things extremely quickly. I also let the eggs sit in a bowl filled with warm water for about 10 minutes, replacing the water every now and then. Warm over to 350 degrees. Spray springform pan . Mix the flour, cornstarch, and baking powder. You don't have to sift flour mixture but you can if you want. In a separate glass container, mix the egg yolks together with the vanilla. Separate the egg whites from the yolks, and beat the egg whites with a pinch of salt till they reach a stiff peak, at which time you add the sugar and continue beating till sugar is well incorporated and the mixture reaches stiff peak. Lower speed of the mixer, and then quickly add the 4 egg yolks (which you can mix together before adding into mixer), then gradually but quickly pour the flour while mixer is on low speed. Stop the mixer, making sure flour is well incorporated, and quickly pour into pan. Bake for 25 minutes. It's a high cake that can be cut in two or three layers. Wait 5 minutes before unmolding cake.

First trick to beat eggs for recipes that require beating and flour to be folded = Let eggs sit in a bowl of very warm water for about 10 minutes. Second trick = the art of folding flour and patience. Google it for a better explanation but it entails cutting through middle of bowl with a spatula and bring batter to the top, then turning bowl to a 15 minute position and repeating process with the spatula. Keep doing this until flour is well incorporated. It can take several several "quarter turns"'so this is why I say patience is important. Also, to make this easier make sure you have sifted flour twice or so.
For me the best sponge cake is a milk sponge cake used in a Boston Cream Pie from baking911.com. If you cannot find it, let me know and i will send it to you. It has milk and oil.

For the bestest and easiest genoise, I have one found in a French website. I will try to paste it here if requested.

I find that butter based cakes with only egg whites give the best of both worlds, as far as lightness and moistness. Genoise can tend to be pretty dry and British-style sponge cakes can be pretty leaden. This is my go-to: http://www.epicurious.com/recipes/member/views/cooks-illustrated-white-layer-cake-50017374

Whenever someone mentions sponge cake, I think of Jack Klompus: https://www.youtube.com/watch?v=JhvzxYMQrQs (not a helpful answer, but a good laugh.)

Nancy is right to steer you to Rose Levy Beranbaum. She's the best.
A really light sponge cake is the result of properly whipping your egg whites [bowl and beaters must be scrupulously clean, there can be no trace of fat (egg yolks that also means you!), whites, bowl and beaters should be at room temperature, then, of course not over-whipping].

Learn from Rose Levy Beranbaum, who is a real expert on cakes and baking.
Whipping the eggs
http://www.realbakingwithrose.com/2010/06/baking_magic_tips_sponge_cakes.html#.VlNHkvmrTIU
Her recipe for genoise (French sponge cake)
http://www.realbakingwithrose.com/recipes/RLB's%20French%20Genoise.pdf
Or, use this reliable orange sponge cake recipe from Julia Child, another great explainer
https://recipes.sparkpeople.com/recipe-detail.asp?recipe=1019355