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Jelly for the Above
One lemon, the juice and half the rind, one large sour apple, grated, one cup sugar; boil five minutes, then let it cool and spread between the cakes.
A tart cooked filling for a layer or "jelly" cake, thickened by the pectin in a grated raw apple rather than by egg or starch. The original assumes you already have the cake layers from the preceding recipe.
- No added liquidThe mixture starts nearly dry — only the lemon juice and the water in the grated apple. Use a heavy saucepan over low to medium heat and stir constantly for the whole five minutes, or the sugar will scorch before the apple breaks down.
- "One large sour apple"A tart, firm cooking apple: Granny Smith, Bramley, Newtown Pippin. Grate it on the coarse side of a box grater, skin and all if unwaxed, and add it to the pan immediately so it does not brown. Expect roughly 1 to 1 1/2 cups.
- Half the rindTake it off with a zester or fine grater and stop at the white pith, which is bitter. Half a lemon's worth of zest is about a rounded teaspoon.
- Why it setsApple is high in pectin, and lemon juice supplies the acid that lets pectin gel with sugar. This is the same chemistry as jam, which is why it firms up only after cooling.
- Judging donenessFive minutes at a real simmer should leave a glossy, thickened mixture that mounds on the spoon rather than running off. If it still looks watery, keep going a minute or two; if it stiffens into a paste, you have gone too far and it will tear the cake.
- Cool completelySpread it warm and it soaks into the crumb and slides. Cool to room temperature, then spread thinly with an offset spatula, leaving a small margin at the edge.
- YieldAbout 1 to 1 1/4 cups — enough for two or three thin layers of an 8- or 9-inch cake, not for a thick filling. Double it if your layers are generous.
- KeepingRefrigerate in a covered jar and use within a week. The sugar and acid preserve it reasonably well, but the grated apple darkens after a day or two.
"Jelly cake" — thin layers of plain sponge or cup cake stacked with a fruit filling between them — was one of the standard American cakes of the second half of the nineteenth century, and cookbooks of the period print fillings under headings like this one, tied to whatever cake recipe sits above. Before commercial powdered pectin was available to home cooks, a grated tart apple was one way to make a small quantity of fruit paste set: the apple supplied pectin, the lemon the acid, and the sugar the rest. The result sits somewhere between a jam and what a modern cook would call a lemon curd, minus the eggs and butter, and it could be made in five minutes from a lemon and an apple.