Pommes de Terre Mousseline

Pommes de terre mousseline (a light potato tart) teaches one precise lesson: air must be folded into richness, not beaten out of it. The potatoes bring body, butter and yolks bring satin, but the whisked cream is what lifts the dome. Before you touch a pan, know this: the potato base must be warm enough to accept the butter and yolks, then cooled until merely warm before the cream goes in.

The original entry assumes a pastry hand could set a pale flan crust beside a cook working the potatoes over the fire, then pass the finished tart beneath a salamander. Your honest equivalents are one 8-inch tart tin, one oven used in stages, and the fierce overhead heat of a household broiler. I have scaled the dish to exactly 1 pound of baked potato pulp for four people, keeping the original proportions intact: 4 ounces of butter, two yolks, and one-sixth of an imperial pint of whisked cream. The separate hands and hot stations were brigade scaffolding, so they can go. The pale shell, dry baked potato, whisked cream, piping, and rapid glaze are the dish, so they stay.

The finished mousseline should stand proud inside its barely colored crust, ivory beneath and delicately golden along the piped ridges, with a crumb that yields softly rather than slumping. Let the potato base cool to merely warm, fold until the last white streak disappears, then stop. That fold is the step that matters most.