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Filling for Walnut Layer Cake
1 cup chopped walnuts 1 cup cream or 2/3 cup sour cream 1 cup sugar 1/4 teaspoon salt 1/2 teaspoon vanilla Mix together all the ingredients except the vanilla, and heat to boiling in a double boiler. Then boil for a few minutes directly over the fire. Beat till cool enough to spread on the cake. Beat in the vanilla.
This is a cooked cream-and-sugar filling in the penuche family: the sugar is dissolved in cream, brought to a soft-ball boil, then beaten until it thickens and loses its gloss. The original gives no thermometer reading, so the sugar stage is the thing to watch.
- The hinge: boil to soft ball"Boil for a few minutes" most likely means boiling to about the soft-ball stage, 234-240F, though the original gives no reading. Much under that and the filling will run off the cake; much over and it sets hard and crumbly before you can spread it.
- Why the double boiler firstHeating over water dissolves the sugar completely and keeps the dairy from scorching. Once it is at a boil and the sugar is fully dissolved, move it to direct heat to drive off water quickly.
- "Cream" hereUnqualified "cream" in a recipe of this date could mean anything from a thin to a rich cream, so fat content is uncertain; a heavy or whipping cream will boil down fastest and most reliably, while half-and-half or light cream carries more water and will take longer to reach temperature.
- The sour cream optionThe acid in sour cream will invert some of the sugar, tending toward a softer, less grainy set, closer to a caramel frosting; the smaller quantity may also reflect sour cream's greater body. Use full-fat sour cream, not low-fat.
- BeatingThe original says to beat until it is cool enough to spread. Modern fudge practice is to let the syrup fall to about 110F before beating in earnest, on the grounds that beating a hot syrup encourages large sugar crystals and a gritty texture.
- Vanilla lastAdding it at the end, off the heat, is deliberate. Vanilla's aromatics boil off, so early addition wastes it.
- Working timeOnce it reaches spreading consistency it continues to firm up fast. Have the cake layers cooled and to hand; if it stiffens too far, a teaspoon of hot cream beaten in will loosen it.
- YieldEnough to fill and thinly top a two-layer 8- or 9-inch cake.
Boiled cream-and-sugar fillings of this kind were common on American layer cakes before butter-and-confectioners'-sugar frostings became the norm in home kitchens. The method is essentially fudge-making stopped short of the point where it sets firm, and walnut versions appear frequently in recipe collections of the late nineteenth and early twentieth centuries. The sour cream alternative would also have suited a household with cream on hand that had begun to turn, since the acidity is no fault in a cooked sweet.