The Mysteries of Sponge Cake, Explained
A favorite of bakers for its versatility, this cake can still be troublesome to make. Our expert advice will help.
Sponge cake may be light and airy, but it's also strong and absorbent, which means it works well with fillings and frostings (like this version with strawberries and Swiss meringue buttercream). It falls squarely in the category of foam cakes, meaning those that obtain their structure and loft from whole eggs (or just the whites) beaten to various degrees of foaminess. (Chiffon and angel food are other familiar foam cakes.) Cake purists insist that sponges rely only on eggs-and the air beaten into them-for leavening, rather than on chemical agents such as baking powder or soda. Yet, as with all rules, there are exceptions.
Defining what is and isn't a sponge cake can be tricky (and somewhat tedious). European examples include genoise (pronounced jen-WAHZ by Americans, and jen-oh-EEZE by Mary Berry, as any Great British Bake Off watcher will tell you) and biscuit (pronounced bis-KWEE, and quite unlike the American rolled and cut pastry of the same name). European sponges may be somewhat dry (they contain very little butter, or none at all), not terribly sweet, and are rarely eaten on their own. Instead, the sponges are rolled into roulades (like Swiss or jelly rolls), cut and layered with custard and cream to make English trifles, stacked and sandwiched with jam to form petits fours, or soaked in espresso syrup for Italian tiramisu.
American sponges are more tender and sweet. (They're also easier to make.) These sponge cakes may be served plain, but they are just as versatile as their European counterparts. Examples include hot-milk sponge (the basis for the curiously named Boston Cream Pie), chocolate sponge (which simply swaps out some of the flour for cocoa powder), and daffodil, or feather, sponge (a marbled, golden-hued delight that has fallen out of favor but is ripe for revival). Yet another example is the nut sponge, popular at Passover because it contains ground nuts in place of flour; other Passover sponge cakes include matzo meal and/or potato starch.
All technicalities (and tedium) aside, sponge cakes are beloved for their versatility. Just as they are adept at showcasing and absorbing different flavors and fillings, they take well to being shaped and molded into dozens of composed desserts. The cooks in the Martha Stewart test kitchen have long been fans of the endless adaptability of sponge cakes.
Advice for Making Sponge Cake
Keep it cool: If your recipe includes butter, melt it and let it cool completely before you begin mixing. If you add warm butter to a carefully beaten, egg-heavy mixture, you will end up deflating the batter and compromising all that careful mixing. And that would be a real shame. (The exception to this, of course, is hot-milk sponge.)
Don't skip the sift: There's lots of debate about whether or not sifting flour is all that necessary. Many modern recipes instruct the baker to simply whisk dry ingredients together in a bowl instead. Yet for sponges and other foam cakes, sifting is significant. (Unless your recipe tells you otherwise. Again, there are always exceptions.)
Mind the eggs patiently: If it's an all egg white sponge, start out slow, then gradually increase the mixer speed once the white are foamy, to allow the egg proteins time to properly build structure. Similarly, if you are beating whole eggs or yolks and sugar together, don't try to rush the mixing. You want the to warm the mixture over hot water until the sugar dissolves, then to beat it until doubled in volume, lightened in color, and most importantly, at the crucial stage where the beaters hold a thick ribbon when lifted from the bowl.
Know how to fold 'em: The key to any good sponge lies in properly folding together the ingredients. Whether you are adding stiffly beaten egg whites to a well-ribboned egg and sugar mixture, incorporating sifted flour into a meringue, or quickly mixing melted butter into a sponge batter, your folding technique is crucial. Remember, deflation is the enemy here-take care to avoid it at all costs. Recipe steps at this stage contain the words "very gently" for good reason. A large flexible spatula will allow you to get incorporate ingredients thoroughly but quickly. And keep this personal anecdote in mind: When I was working with editorial food director Sarah Carey, editing Martha Stewart's Cooking School, she taught me this: When it comes time to fold, cut the spatula down through the center, then use a sweeping motion up the side of the bowl and turn the spatula over (as if making the letter "J"), rotating the bowl as you go. I've heeded Sarah's advice every time since then and I haven't suffered a sunken sponge since.