Lemon-Cake Pie

A self-separating pudding cake baked in a pastry shell: the batter goes in as a thin liquid and comes out in two layers. A few unstated steps are hiding inside the phrase "mix as for cake."

• What "mix as for cake" meansCream the butter with the sugar, beat in the yolks, then the flour, then the milk and lemon. Beat the two whites to soft peaks separately and fold them in last. The folded whites are what float to the top and set as the sponge layer; stir them in and you get one dense custard instead of two layers.
• The batter is meant to be thinOne tablespoon of butter to a cup of milk gives a pourable, slightly curdled-looking mixture. The lemon juice will curdle the milk on contact. Neither is a fault and neither needs correcting.
• SaltNone is listed. A pinch in the batter and another in the crust sharpens the lemon considerably.
• Lemon quantity"1 lemon" is unquantified; roughly 3 tablespoons of juice and a packed teaspoon of zest is a workable reading, and a very large modern lemon can overwhelm one cup of milk.
• The crustA wet batter in a raw shell will soak the bottom unless the initial heat is fierce. Use a metal or glass deep dish, chill the lined tin while the oven comes up, and set it on a preheated baking sheet on a low rack for the 450F stage.
• Oven stagingTen minutes at 450F to set the pastry, then 25 minutes at 350F. Move the pie to the middle rack when you drop the heat, and tent the rim with foil if the crust edge is already brown.
• DonenessThe sponge top should be golden and spring back at the center; the pie will still wobble as a whole because the custard layer stays soft. Cool at least an hour before cutting or the layers slump together.
• Yield and keepingThe recipe says only "deep pie tin"; the quantities suit one 8- or 9-inch deep pie, six to eight servings. Because the lower layer stays soft and custardy, refrigerate leftovers and eat within two days.