Cream Filling
7/8 cup sugar 1/3 cup flour 1/8 teaspoon salt 2 eggs 2 cups scalded milk 1 teaspoon vanilla or ½ teaspoon lemon extract Mix dry ingredients, add eggs slightly beaten, and pour on gradually scalded milk. Cook fifteen minutes in double boiler , stirring constantly until thickened, afterwards occasionally. Cool and flavor.
This is a standard pastry cream (crème pâtissière) in Fannie Farmer's shorthand: no butter, thickened with flour rather than cornstarch, and cooked over water so it cannot scorch. It works as written, with a few notes.
- 7/8 cup sugarThat is 1 cup less 2 tablespoons, about 175 g.
- Scalded milkHeat the milk until it steams and small bubbles ring the pan, roughly 180F, then take it off. Adding it gradually to the egg-and-flour paste is the whole point of the step — it tempers the eggs so they thicken rather than scramble.
- Flour, not cornstarchFlour gives a softer, slightly cloudier set than cornstarch and needs the full cooking time to lose its raw taste. If you substitute cornstarch, use about half as much and stop cooking soon after it thickens, since cornstarch thins if overworked.
- The fifteen minutes is realUnlike many old timings, this one should not be cut. A double boiler never reaches the temperature of direct heat, so the custard needs the time both to set and to cook out the flour. Stir constantly until it thickens or the flour will lump at the bottom.
- Straining and coolingPush the finished cream through a sieve while hot to catch any set egg, then press plastic wrap or buttered paper directly onto the surface.
- Flavour lastThe recipe adds the extract after cooling. Alcohol-based flavourings lose aroma in a hot pan. Fold them in when the cream is barely warm.
- YieldAbout 2½ cups, enough to fill and layer a two- or three-layer 8- or 9-inch cake, or roughly a dozen cream puffs. Refrigerate and use within two days; being egg and milk, it does not keep.
Filling a plain butter cake with a milk-and-egg custard rather than icing it is often said to have been a New England habit before Fannie Farmer wrote it down, and the resulting "cream cake" or "Boston cream cake" is popularly associated with Boston cream pie — a name generally traced to the days when cakes were baked in pie tins. The technique itself is French pastry cream, standardised here for a cooking-school audience: exact fractions of a cup, a double boiler instead of a copper pan and a practised wrist, and a timing anyone could follow. That flattening of professional method into reproducible household instruction is the whole editorial project of the Boston Cooking-School Cook Book.