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Plain Frosting
White 1 egg. 2 teaspoons cold water ¾ cup confectioners' sugar ½ teaspoon vanilla or ½ tablespoon lemon juice Beat white of egg until stiff; add water and sugar. Beat thoroughly, then add flavoring. Use more sugar if needed. Spread with a broad-bladed knife.
Chocolate Frosting I 1½ squares chocolate Yolk 1 egg 1/3 cup scalded cream Few grains salt ½ teaspoon melted butter Confectioners' sugar ½ teaspoon vanilla Melt chocolate over hot water, add cream gradually, salt, yolk of egg, and butter. Stir in confectioners' sugar until of right consistency to spread; then add flavoring.
This is an uncooked egg frosting of the sort that filled cookbooks before refrigeration and food-safety testing changed the advice. The measurements and method are easy enough to read; the raw egg is the problem.
- Why it failsBoth frostings here rely on raw egg — the white in the plain frosting, the yolk in the chocolate — and neither is ever brought to a temperature that would kill Salmonella. Scalded cream poured over a yolk off the heat does not get there either, and a frosting sits at room temperature on a cake for hours, which is exactly the condition the bacteria prefer.
- Not an ordinary kitchen riskRaw egg in a batter is fine because the oven finishes the job. A spread that goes onto a finished cake and is eaten as-is has no such step. Use a current frosting recipe instead.
- Confectioners' sugarFinely powdered sugar; modern commercial versions are cut with a little cornstarch to stop caking. The instruction to add "more sugar if needed" leaves the cook to judge spreading consistency rather than work to a fixed weight.
- Squares of chocolateA "square" is one ounce of unsweetened baking chocolate, still sold in scored bars. It is bitter and unsweetened — the sugar in the recipe is doing all the sweetening.
- Broad-bladed knifeThe period tool for spreading frosting; an offset icing spatula is the modern equivalent and does the same work with less drag on the crumb.
- Scalded creamHeating cream just to the point where it steams and bubbles form at the rim, conventionally reckoned at somewhere near 180F; the book gives no temperature. Scalding was long-standing practice with unpasteurised dairy and also warms the cream so it blends smoothly into the melted chocolate.
Frostings in the era of The Boston Cooking-School Cook-Book divided into boiled and uncooked types, and the uncooked ones needed no thermometer and no sugar syrup taken to a soft-ball stage — just an egg beaten stiff and sugar worked in until it would hold a swirl. Fannie Farmer's book is known for level measurement, and a frosting that could be made in the time it took a cake to cool was a practical convenience. The advice against raw egg came later, as attention to commercial egg supplies in the twentieth century made the risk plain.