Orange Filling

This is a variation entry rather than a standalone recipe: it assumes the lemon filling printed alongside it, which is a cornstarch-and-egg cooked filling of the standard type. The only figure given here is the reduced sugar.

• The missing base recipeThe entry depends entirely on the lemon filling printed with it, which is not reproduced here; cooked fillings of this period typically combine sugar, a thickener such as cornstarch, an egg or yolk, hot water, and the rind and juice of the fruit. The instruction changes the fruit and gives ½ cup sugar. Work from whichever lemon filling the book gives, not from a modern lemon curd, which is a butter-and-yolk emulsion and behaves differently.
• Why less sugarWhy the sugar is restated -- Orange juice is sweeter and much less acidic than lemon, so a filling built for lemon can taste flat made with orange; the ½ cup is the one figure the entry bothers to give. If your oranges are very sweet, a teaspoon of lemon juice restores some edge without changing the character.
• Juice quantity is variableOne orange yields roughly twice the juice of one lemon — about ¼ to ⅓ cup against 2 to 3 tablespoons. Measure rather than substituting fruit for fruit, and if the base recipe uses water, cut it back by whatever extra juice you add, or the filling will be slack.
• Rind means zestGrate only the coloured outer layer. The white pith beneath is thick and bitter, and a heavy hand with the grater will show.
• The hinge: boil the cornstarchCornstarch does not reach full thickening power until the mixture actually bubbles, and it needs a minute or so at that point. Pulled off early it sets thin and tastes chalky. Add the juice at the very end, off the heat — prolonged boiling with acid breaks cornstarch down and thins the filling again.
• Tempering the eggIf the lemon filling includes an egg, whisk a ladle of the hot thickened mixture into the beaten egg, then return it all to the pan and cook gently for another minute. Adding the egg cold and direct will scramble it.
• Cool before spreadingCover the surface with waxed paper or plastic against the filling itself so no skin forms, and cool to room temperature. Spread warm, it soaks into the crumb and slides out of the layers.
• YieldA one-cup base of this kind fills a single layer between two 8- or 9-inch cakes. Refrigerate anything you make ahead, and use within two days — it contains egg.