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Potato Cups
These are easily made by adding one egg yolk to one cup well-seasoned mashed potato. The potato should be slightly warm. This amount will make four cups. Invert any custard cups or jelly-glasses and cover the outside, bottom and two inches up the sides with the potato mixture.
Smooth over and set away to get cold. When ready to use turn right side up on a well-buttered flat pan and very carefully remove the molds.
Brush the outside with beaten egg and milk before adding the fish.
A shaping technique rather than a dish in itself: the potato is molded over inverted cups to make edible cases for creamed leftover fish. Two details decide whether it works.
- The hinge: chill until firmThe molded potato must go cold and stiff before you attempt to lift the cups away, and warm potato will slump the moment the glass is withdrawn. An hour in the refrigerator is enough; overnight is better.
- Potato consistencyUse stiff, dry mashed potato made from a floury variety (russet, Idaho) with little or no milk. Anything loose or waxy will not hold a wall two inches tall.
- Slightly warm, not hotThe potato needs to be warm enough to spread smoothly but cool enough not to cook the yolk into strings. Around body temperature.
- The moldsCustard cups and jelly glasses of the period were small vessels of no fixed capacity, roughly four to eight ounces. Any straight-sided ramekin, small bowl or wide-mouthed jar of about that size works; it is removed before the cases go in the oven, so it need not be heatproof. Butter or oil the outside of the mold lightly, which the original omits and which makes release far easier.
- Egg washBeaten egg thinned with a little milk, brushed on before filling, sets into a shell that browns and helps the cases keep their shape in the oven.
- BakingThe recipe never actually says to bake; the buttered flat pan and the egg wash only imply that the filled cases went into an oven. No temperature or time is given, and any figure here is a guess: a fairly hot oven for a short spell is enough to color the outsides without drying the potato.
- The fillingThe recipe says only 'the fish', presumably cooked and most likely bound in a sauce, though it does not say so. Fill the cases only when the filling is already hot and fully cooked; the short spell in the oven browns and warms, it does not cook raw fish.
- YieldOne cup of mashed potato and one yolk make four cups, by the recipe's own reckoning.
Left-over cookery was a whole genre of American and British household writing from the 1880s through the First World War, and its central problem is often said to have been presentation: a cook needed cold fish or yesterday's roast to arrive at the table looking deliberate rather than salvaged. Potato borders, potato roses piped through a bag, duchesse potato baskets and molded cases like these were the standard answer, borrowed from professional kitchens where pommes duchesse (mashed potato enriched with egg yolk) had long been used as an architectural material. The yolk is not there for flavor but for structure, since it sets on heating and stiffens the wall.