With Sponge Cake, the Devil is in the Details

I made a sponge cake, which for those not in the know, is a cake who's only form of aeration/rising comes from beating eggs, and which contains no fat such as shortening or butter.

On Food and Cooking lists the appropriate ratios for a sponge cake to be (by weight):
100 parts flour,  225 parts egg, 155 parts sugar.
In Fannie Farmer there was a recipe with 1 cup flour, 5 eggs, 1 cup sugar, 1 tbspn lemon juice, 1/4tsp salt, which is approximately 100, 212, 160.

I decided to make half this recipe (1 8-inch pan), but used 3 eggs so I had a ratio of 100, 250, 160.  I followed the instructions and the cake came out springy, but too thin.  So then I said to myself: "Danielle, you should make a second one!"

I set to make a list of things that might have gone wrong (and for some reason didn't notice the obvious excess of egg). This was my list:

1. I greased the pan (apparently with sponge and angel food you don't so that it acts as a lattice/support for the cake to "climb").
2. My new cake pans I bought are dark colored (light is better for even cooking).-- I can't change this.
3. My sugar was too granular / not fine enough.
4. The folding order in the recipe seemed sub-optimal (egg whites into yolks, then flour into all)

OK, here's my new recipe for a single 8-inch round:

Put 1/2 cup sugar in a coffee grinder or food processor and grind the the consistency of corn starch.

Beat the yolks of 3 eggs with 1.5 tspn lemon juice, add 3/8 cup sugar~, and continue to beat until creamy and pale, then set aside.

Whisk 3 egg whites until foamy, add salt followed by remaining 1/8th cup sugar, and beat until stiff peaks have just formed.

Sift .5 cup cake flour over the egg yolks and fold in slowly.

Then fol in the egg whites, and scoop into an ungreased 8-inch spring form cake pan.

Bake at 325F for 25min.

The new recipe was obviously fluffier when layered into the pan.  In the picture of the slice below, the first attempt is the bottom, and the second is the top.  Not only does the new recipe give more volume, everyone agreed it tasted MUCH moister.  

For those curious about the frosting and filling, they are made from stuff in my fridge.  I had some failed strawberry jam (forgot the pectin).  i put it between the layers and then mixed the remainder with mascarpone cheese and whipping cream on high in my kitchenaid.  It was quite yummy, even though I ran out and so it looks a bit sad..

For Next Time:

Make both 8-inch rounds in one 5 egg recipe, matching all ingredients to exactly 100, 225, 155.

Formulate a low-fat ricotta and fresh berry frosting with minimal sugar.

Buy and use an oven thermometer.