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White Potato Pie
To one cup of mashed potatoes add one pint of milk and the yolks of three eggs, well beaten. Mix and add one cup of sugar and the juice and rind of one lemon. Turn this into a deep dish lined with paste, bake in a quick oven thirty minutes. Beat the whites of the eggs until light, add three tablespoonfuls of powdered sugar and beat white and stiff. Heap this over the pie, put back in the oven a few moments to brown.
A sweet potato custard pie in the older sense — the potato is a thickener and body, not a flavour. Success turns on treating it as a custard rather than a pie filling.
- The hinge: don't overbakeThis is a milk-and-yolk custard, and thirty minutes at a true "quick" heat will curdle it. Bake until the filling is set at the edge and still barely wobbles in a two-inch circle at the centre; carryover heat finishes it while the meringue browns.
- "A quick oven"Period sources generally put this around 400–425F. The recipe gives no second temperature; if you are blind-baking the shell, start hot, but a milk-and-yolk custard is more reliably baked down at 325–350F, which is a modern adjustment rather than what the text specifies.
- MeasuresA pint is 2 cups of milk to 1 cup of mashed potato. Whole milk gives the texture intended; skim makes a thin, watery custard.
- The potatoesThe recipe specifies nothing beyond "mashed potatoes." Plain boiled and mashed, unseasoned, suits the sugar and lemon best; heavily buttered or salted leftovers will pull against them. Press through a ricer or sieve so no lumps survive into the custard, and let them cool before the milk goes in.
- Paste and soggy bottoms"Lined with paste" means a single bottom crust, no top. A wet custard filling needs the shell partly blind-baked — about 15 minutes with weights — or the base never crisps.
- Lemon rindGrate only the coloured zest of the lemon; the white pith underneath is bitter. Rub the zest into the sugar first to draw out the oil.
- The meringueThree tablespoons of sugar to three whites is a soft meringue and will weep if it sits. Spread it while the filling is still hot and take it right out to the crust edge to seal it. The recipe asks only for "a few moments" in the oven to brown; a moderate heat and a watchful eye serve better than blasting it.
- YieldThe recipe calls only for "a deep dish"; the quantities suit roughly a 9-inch deep pie, six to eight servings. Cool at least two hours before cutting; a warm custard pie slumps on the plate.
The qualifier "white" is the whole point of the title: "potato pie" was often taken to mean sweet potato, so cooks specified the white or Irish potato when they meant this paler, milder version. Both belong to a large family of sweet vegetable custards — pumpkin, squash, carrot, sweet potato — in which a starchy purée stands in for some of the eggs and gives the filling body at low cost. Recipes of this type are generally traced to English potato and carrot puddings of the eighteenth century, and they survived in American cookbooks partly out of thrift: a cup of yesterday's mashed potato, a lemon and some sugar made a dessert without recourse to anything expensive.