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Mocha Frosting
2 eggs 1½ cups scalded milk 1 cup strong coffee 2 squares chocolate (melted) 1 teaspoon vanilla 1½ cups confectioners' sugar 4 cup flour 1 cup granulated sugar 1 teaspoon salt Cream butter; add confectioners' sugar. Beat eggs; add granulated sugar, flour, salt, milk, coffee and chocolate. Cook in double boiler ten minutes; cool, flavor, and add to creamed butter. Use for filling and frosting for mocha cakes.
This is a cooked custard base folded into creamed butter — closer to a French buttercream than to a stir-together frosting. The custard is where it succeeds or fails.
- Butter is called for but not measuredThe method opens with "Cream butter" and no quantity appears in the ingredient list, apparently an omission in the printing. The original text gives no figure, so treat the amount as unspecified rather than assuming one.
- Chocolate squaresA square meant 1 ounce of unsweetened baking chocolate, so 2 squares is 2 ounces. Lowney's sold baking chocolate in that form, which is presumably why the book measures in squares. Melt it gently and let it cool slightly before it goes into the egg mixture.
- Scalded milkHeat the milk to about 180F, until it steams and a ring of small bubbles forms at the edge, not to a boil. With raw milk scalding helped keep it from souring and turning the custard; with pasteurised milk it mainly speeds the custard along.
- Cooking the custardTen minutes over simmering water is a guide, not a rule. Cook until the mixture coats the back of a spoon and has thickened; the flour in the mixture makes it more forgiving of heat than a plain egg custard, but very high heat will still give a grainy result. Stir constantly and keep the bowl clear of the water below.
- Cool it completelyThe custard must be at room temperature or cooler before it meets the creamed butter. Warm custard melts the butter and the frosting separates into a soupy mess that no amount of beating will bring back.
- Strong coffee"Strong coffee" in a book of this period would have been a stovetop or percolator brew. Brewed espresso or double-strength drip works; the liquid volume is doing structural work, so do not substitute a spoonful of instant granules without making up the cup.
- Consistency and yieldThis should make roughly enough to fill and frost a two-layer 8- or 9-inch cake, though the unmeasured butter makes the yield approximate, and it sets softer than a plain butter icing. If it is loose after beating, chill it fifteen minutes and beat again.
- KeepingAn egg-and-milk buttercream is perishable. Refrigerate the finished cake and bring it back to cool room temperature for an hour before serving so the butter softens.
Lowney's Cook Book was published by the Walter M. Lowney Company of Boston, a chocolate manufacturer, and like most branded cookbooks of its era it exists to move product. "Mocha" here means what it usually meant around 1900: coffee, or coffee and chocolate together, the name borrowed from the Yemeni port of Mocha that had been the byword for fine coffee since the seventeenth century. Mocha cakes and mocha fillings were a fixture of American and European pastry counters in this period, and the technique behind this one — a cooked custard beaten into creamed butter — is the same principle as a French buttercream, giving a filling stable enough to hold between layers in a warm dining room without the brittleness of a boiled sugar icing.