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Maple Filling
1/2 C maple sugar. 1/2 C hot water 2 egg-whites 1 scant C granulated sugar Let boil until it strings well.
Then beat quickly into the beaten whites of two eggs.
This is a boiled icing — hot sugar syrup whipped into beaten egg whites — written in the shorthand of a cook who already knew the method. The title is the only place maple appears, which tells you something about how these church-book contributions were edited.
- The missing mapleNothing in the ingredient list is maple. Other fillings of this name generally relied on maple sugar, or a mix of maple and white sugar, in place of the granulated; grated maple sugar or firmly packed maple crystals substituted cup for cup should give the flavour the title promises. Maple syrup alone will not work here without recalculating the water.
- "Until it strings well"This is the visual test for the thread stage — a spoon lifted from the syrup trails a fine thread — usually placed somewhere around 230F. Boiled icings tend to hold better if the syrup is taken a little further, into the soft-ball range (roughly 235-240F), so a thermometer is worth using; cooked too low, the filling stays loose and weeps.
- A scant cupSlightly under a level cup, roughly 6 1/2 oz of granulated sugar. "Scant" and "heaping" were common qualifiers in period measuring, though how precisely any given cook meant them is not recoverable.
- Beat quickly, but pour slowlyThe hinge of the recipe. The syrup goes into whites already beaten to soft peaks, in a thin steady stream down the side of the bowl, with the beater running the whole time. Dumped in at once it cooks the whites into threads and the filling will never smooth out.
- Egg safetyThe hot syrup warms the whites but will not reliably bring them to a pasteurising temperature, so this should be treated as a raw-egg-white preparation. If you are serving anyone vulnerable, use pasteurized whites, allowing that they may take longer to whip up.
- Beat until coolThe original stops at "beat quickly." Keep going until the bowl is no longer warm to the touch, five to eight minutes with a stand mixer, or the filling will slump between the layers.
- YieldTwo whites and a cup of sugar should make roughly enough to fill and thinly top a two-layer 8-inch cake. It sets to a marshmallow crust fairly quickly and keeps poorly, so assemble the cake the day it is served.
- WeatherBoiled icings are notoriously reluctant on humid days. Cook the syrup two or three degrees higher when the kitchen is damp.
Boiled icing — Italian meringue by another name — was a common American cake finish, and it turns up in period community cookbooks under names like white mountain cream or, as here, a flavour plus "filling." The maple version is generally traced to the upper Midwest and the Northeast, where maple sugar was a household staple sold in cakes and grated as needed. Libertyville sits in Lake County, Illinois, well inside the region where a cookbook's contributors would be assumed to know what "strings well" looked like and what a maple filling was supposed to taste like — which is presumably why nobody caught that the maple never made it into the ingredient list.