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Philadelphia Potatoes
Cut into half-inch dice sufficient cold boiled potatoes to measure 1 pint. Make a white sauce by putting in a saucepan 1 tablespoonful of butter, 1 tablespoonful of flour, ½ of a teaspoonful of salt and ¼ of a teaspoonful of white pepper.
Stir until mixed, then add gradually ½ of a pint of hot milk, and continue stirring until thick and smooth. Put potatoes and sauce in alternate layers in a baking dish, pour over the top 1 wellbeaten egg, and brown in a hot oven.
A thrifty way to use up leftover boiled potatoes: diced potato layered with a basic white sauce, glazed with beaten egg and browned. It comes together in about twenty minutes once the potatoes are cold.
- Quantities in modern termsA pint of diced potato is 2 cups, from roughly three-quarters of a pound of potatoes boiled ahead and left to go cold. The sauce uses 1 cup (half a pint) of hot milk against 1 tablespoon each of butter and flour.
- Cold potatoes are the pointFreshly boiled potatoes crumble when diced and turn the dish to mash. Chill them thoroughly first so the half-inch cubes hold their shape through baking.
- A hot ovenRead this as 425-450F. The dish is already cooked through, so all the oven does is set the egg and colour the top; 15 to 20 minutes is usually enough.
- The sauce is thin by designOne tablespoon of flour to a cup of milk gives a pouring sauce, not a thick binder. That is correct here, since the potatoes absorb liquid as they heat.
- The egg glazeBeat the egg well and pour it over the surface only. It sets into a thin browned skin, closer to a gratin top than a custard; do not stir it through the layers.
- SeasoningHalf a teaspoonful of salt, with a quarter teaspoonful of white pepper, is modest for the whole dish, especially if the potatoes were boiled without salt. Taste the sauce before assembling. White pepper keeps the sauce pale, but black pepper does no harm.
- YieldEnough for three or four as a side dish. The recipe says only 'a baking dish'; a shallow one of about a quart suits the volume, and a wider dish gives more browned surface.
White sauce with leftovers was a staple of economical cookery around the turn of the twentieth century, when household manuals treated the reuse of cold vegetables and meats as a matter of thrift rather than a compromise. Dishes carrying city names in these books, Philadelphia and Boston among them, often cannot be traced to any particular local practice, and the name may signal little more than a familiar style. What distinguishes this version from ordinary scalloped potatoes is the beaten egg poured over the top in place of buttered crumbs, giving a glazed brown surface without the cost of bread or extra butter.