Antique Recipe for Sea Foam Icing

Sea foam icing earns its name honestly: it is light, billowy, and marshmallowy, with the soft caramel flavor that only brown sugar can give. This is old-fashioned cake frosting at its airiest.

The technique is a classic meringue trick. Brown sugar and water boil into a hot syrup, which then gets drizzled slowly into beaten egg whites while you beat without stopping. That stream of hot syrup gently cooks the whites, whipping them into a glossy, stable foam.

Getting the syrup right is key. Boil it without stirring until it spins a thread off the spoon, the old-fashioned cue that it has reached the right concentration to set the icing.

Pour it in slowly and steadily. Dumping the hot syrup in all at once cooks the whites unevenly and can deflate the foam you are working so hard to build.

Spread it between and over cake layers while it is still fluffy and pillowy, before it begins to set.

Pro Tips

• Boil the syrup without stirring to keep sugar crystals from forming and making the icing grainy.
• Add the hot syrup in a slow, steady stream while beating constantly so the whites whip up stable.
• Use the icing right away, since boiled frostings firm up and become hard to spread as they sit.
• Frost a fully cooled cake so the icing does not melt or slide.

Variations

• Add a splash of vanilla or a pinch of cinnamon for extra warmth.
• Fold in chopped toasted pecans for a praline-like finish.
• Use it to fill and frost a spice cake or banana cake for a caramel pairing.