A perfect sponge cake—for Passover or otherwise—should be easy and fun to make. If this has not been your experience, or you want to improve an already good recipe, read on.
A typical sponge cake with separated eggs works like this: Separate the eggs, beat yolks with all or most of the sugar in a stand mixer until pale and light, then add any liquids, citrus zest, and flour (or matzo cake meal). Scrape it all into to another bowl. Wash and dry the mixer bowl and beaters thoroughly before whipping the eggs whites—they need to be absolutely grease free, or the egg whites won't beat. Fold mixtures together, etc. Some recipes eliminate the bowl washing interruption by whipping whites first and transferring them to the second bowl, then beating the yolks in the unwashed mixer bowl—since traces of egg white won’t hurt the yolks.
Either way, I’m not happy. I like to mix a cake in a graceful series of uninterrupted steps that do not include stopping to degrease utensils! Nor do I allow egg whites to wait—even briefly while beating another mixture—lest they lose the moisture and elasticity needed for perfect folding and a truly light cake.
My way works like this:
Use a hand mixer to beat the yolks with the salt and sugar in a bowl that's large enough to fold all of the batter together later. Put egg whites in the bowl of a stand mixer, adding 1/4 teaspoon of cream of tartar, or 1 teaspoon of either lemon juice or white vinegar for every 4 egg whites. As soon as the egg whites are ready (as described in your recipe), fold them into the yolk mixture—not vice versa— in the larger bowl.
I use a hand mixer and a stand mixer, because it’s easier, produces better results, and gets rid of a tedious, interruptive step.
I beat salt with the yolk and sugar mixture instead of adding it with the flour—so the yolks emulsify and whip up faster.
I stabilize my egg whites with something acidic, like cream of tartar, lemon juice, or vinegar. (For more info on why this is important, see our prelude to beating egg whites.)
And finally, batter goes in pan, and pan goes in oven. Cool as directed.