The batter of this dessert is homogenous when put into the baking dish, but then magically divides during cooking into a layer of quivery custard on the bottom and a light and spongy cake on top. If you serve it from the dish, the sponge will form a decorative top, or you may unmold it. If you prefer a meringue-like quality for the topping, reserve ¼ cup of the sugar to beat slowly into the stiff egg whites before folding them into the egg yolk mixture.

Preheat the oven to 325°F. Lightly butter a 9 × 2-inch round cake pan or six 6-ounce custard cups or ramekins.

Combine in a medium bowl and mash together with the back of a wooden spoon:

Beat in:

Add and mix until smooth:

Gradually beat in:

Stir in:

Beat in a large bowl on medium-high speed until stiff but not dry:

Gently whisk the whites into the milk mixture, blending just until no large lumps of whites remain. Ladle (do not pour) the batter into the prepared pan or cups; it may reach the top. Set the custards in a deep pan large enough to accommodate them without touching each other or the sides of the pan. Set the pan on a pulled-out oven rack and add enough scalding-hot tap water to come one-half to two-thirds of the way up the sides of the custards. Bake until the tops are puffed and golden brown and spring back when pressed lightly with a finger, 30 to 40 minutes for both small and large custards. Let stand for 10 minutes in the water bath. Serve warm, at room temperature, or chilled, in the mold(s) or turned out. If you wish, accompany with: