Sea Foam Icing
1 cup brown sugar 1/3 cup water white of 1 egg Put sugar in saucepan with water; stir until sugar is melted; then put over fire and boil until syrup spins a thread. Beat white of egg until dry and add hot syrup slowly, beating all the time. When it foams, put between layers and on top of cake.
This should be beaten with wire whip on a platter, not in a bowl.
A boiled brown-sugar meringue frosting, essentially an Italian meringue made with brown sugar rather than white. The hinge is the syrup: too cool and the icing never sets, too hot and it turns to fudge on the whip.
- "Spins a thread"That is the thread stage, 230-235F on a candy thermometer. A drop lifted on a spoon should trail a fine thread a couple of inches before breaking.
- Pour slowly, off the whiskAdd the hot syrup in a thin stream against the side of the vessel, not onto the beaters, or it will fling into strings and set hard on the wires. Keep beating continuously until the mass is thick, glossy and no longer warm to the touch.
- The platterBeating on a wide platter rather than in a bowl was practical advice for a hand whip: it spreads the icing thin so it cools fast and gives a whisk room to work. With a stand mixer the bowl is fine.
- Brown sugarPeriod brown sugar was less uniform than today's. Light brown gives the pale caramel colour the name implies; dark brown works but reads as butterscotch and can weep slightly. Pack it when measuring.
- "Beat white of egg until dry"Meaning stiff peaks, dry-looking and not sliding in the bowl, but not so far that it goes granular and separates. One large white is right for this quantity.
- Egg safetyThread-stage syrup poured over a beaten white will not reliably bring the mixture to 160F throughout. Pasteurized whites, sold in cartons, whip adequately and remove the question.
- WeatherBoiled icings are humidity-sensitive. On a damp day the syrup absorbs moisture and the icing stays tacky; cook to the top of the range, 235F, if the kitchen is humid.
- Yield and useRoughly enough to fill and top one 8- or 9-inch two-layer cake, thinly. Spread while still soft; it crusts fairly quickly and is difficult to smooth once it does.
Boiled icings of this kind spread through American cookbooks in the later nineteenth century, once reliable granulated and refined sugars were cheap and the syrup stages were common kitchen knowledge. "Sea foam" was applied loosely to brown-sugar confections of aerated egg white, covering both this frosting and the candy of the same name, which is divinity made with brown sugar; the name is often said to describe the pale, bubbled, quickly setting mass. Frostings of this type suited the cake chapter of a cheap cookbook, using no butter and costing little beyond one egg and a cup of sugar. The instruction to beat on a platter is a reminder of how much of this work was done by arm, with a coiled wire whip, before domestic electric mixers were common.