Sunshine Cake (C Swans Down flour sifted)

The transcription here has run several contributors' entries together, so read the ingredient line with care before you start. What follows is a yolk-and-white foam cake with no chemical leavening at all: everything depends on how much air you beat into the eggs and how gently you fold.

• The garbled ingredient listThe trailing "1 C sugar 1/2 C butter 1/2 C sweet milk" almost certainly belongs to an adjacent recipe rather than to this one: a butter-and-milk batter is incompatible with an angel-tin foam cake. The sunshine cake proper is flour, whites, yolks, lemon juice and sugar.
• The missing sugar quantityThe instructions say to sift sugar with the flour and to add sugar to the yolks, but no amount survives in the text. Printed sunshine cakes of roughly this size (eleven eggs to 3/4 cup flour) generally call for somewhere between 1 and 1 1/2 cups of sugar; a cup is a reasonable reading, but the original is genuinely silent.
• Swans Down flourA soft-wheat cake flour, still sold under the same name. It is lower in protein than all-purpose and is what gives the crumb its tenderness. If substituting all-purpose, remove 2 tablespoons per cup and sift repeatedly as directed.
• Sift four times, and mean itWith no baking powder, the sifting is structural: it aerates the flour and keeps it light enough to fold into the foam without deflating it. Sift the sugar with it as written, then fold in a third at a time.
• The beating times are for a hand whiskSeven minutes on the yolks and eleven total on the whites assume an arm and a wire whisk. A stand mixer reaches the same stage far sooner — whip the yolks until pale, thick and ribboning, and the whites to firm but still glossy peaks that are not dry.
• Cold eggs and cold bowlsAn unusual instruction, since cold whites are harder to whip; the reason the original gives none, though a cold foam is slower to break down over a long hand-beating. What does matter is that the bowl be scrupulously grease-free.
• Oven temperatureNone is given. A moderate oven, around 325F, suits foam cakes of this type in a modern range; the instruction not to let it brown within twenty minutes is the original's way of saying the oven must not be hot.
• The tin must be ungreasedAn "angel cake tin" is a tube pan, often with a removable bottom. The batter climbs the sides as it rises, so no grease and no flour, or it will slide back down.
• Inverting to coolTurn the pan upside down the moment it leaves the oven — over a bottle neck if the pan has no feet — and leave it until completely cold. A warm cake left upright compresses under its own weight. Batter of this size suits a 9- or 10-inch tube pan; the original specifies no size.