Potato Pie (Mashed potatoes raised)

This is less a recipe than a shape: a wall of stiff mashed potato built up into a case, browned in the oven, and filled at the last moment with something already cooked. Everything depends on the potato being dry enough to hold its own edges.

• The hinge: dry, stiff mashUse a floury potato, steam or bake rather than boil where you can, and dry the mash over low heat before beating in butter and an egg yolk or two. Milk-loosened mash will slump in the oven and the scalloped rim will disappear.
• Building the caseShape the potato into a wall on an ovenproof dish, or pipe it, and cut the scalloped top with the back of a knife or a spoon. Chill the shaped case for half an hour before it goes in the oven so the pattern holds.
• OvenThe recipe says only 'browned'. In a modern oven a hot setting, roughly 400-425F, will set the case and take colour in twelve to twenty minutes; a slower oven tends to dry it out before it browns.
• Egg washYolk beaten with a spoonful of cream or water gives the gloss. Brush thinly, or the wash pools in the scallops and scorches.
• "Done white"Period shorthand for cooked without browning, in a pale sauce -- veal gently poached and bound with a béchamel or velouté, the same idea as a blanquette. No colour on the meat, no brown gravy.
• "Small potatoes scooped out of old ones"Not new potatoes: balls cut from large old ones with a scoop, boiled and finished in cream. Genuine small new potatoes were a seasonal item, which is presumably why the recipe specifies old ones.
• Fill hot, serve at onceThe filling should be fully cooked and hot before it goes in, since the oven time is for browning the shell alone. Assemble as it leaves the kitchen or the potato absorbs sauce and collapses.
• "Top dish"It was meant for the head of the table in a course served all at once, not as a main course on its own. The recipe gives no quantities; proportions and yield are left to the cook.