Just a simple, classic sponge cake. I made cupcakes. I used lemon juice instead of vinegar. The yolk and sugar mixture was really stiff. Not only was it butter-colored; it had the texture of thick butter mixed with sugar, so that when the flour was added the resulting texture was very stiff like shortbread dough. Then I had to mix the delicate egg whites into this! I was convinced they were going to collapse. In fact, the cakes rose beautifully. There were a few streaks of thicker egg-yolk batter in the cakes. For the most part, though, they had quite a nice flavor and texture. This recipe had no aftertaste of chemical leavening, and, unlike recipes I have tried that included hot water or hot milk, it wasn't the least bit sticky.