Lemon Puff

A lemon curd base lightened with beaten whites, in the manner of a cold souffl called a "puff." The method has one step that current food-safety practice rules out, and it is not a small one.

• The whites are never cookedTen egg whites are beaten stiff and folded into the finished curd, which is then served as is. Folding cold foam into a thick custard drops the mixture well below any pasteurising temperature within seconds, and the aerated structure insulates rather than conducts. Nothing in the dish brings those whites to a temperature that would reduce Salmonella, and the volume of raw white here is large relative to the cooked base. A current recipe using pasteurised whites, or a cooked meringue, should be used instead.
• The curd itself is the safe partYolks, sugar, lemon juice and water cooked over a double boiler until smooth and very thick will normally have reached somewhere in the region of 170F by the time they thicken, though the recipe names no temperature. That portion of the method is the sounder part; the failure is in what is added afterward and not returned to heat.
• Why the acid does not rescue itLemon juice is often assumed to sterilise. It does not. The whites are folded in after the acid has already been diluted by ten yolks, a cup of sugar and water, and there is no holding time at any temperature.
• Cupful and tablespoonfulFor reading the proportions: the cupful is 8 fl oz and the tablespoonful about 1/2 fl oz, so the base is roughly ten yolks, 200 g sugar, 45 ml water and the juice of two lemons, perhaps 60-90 ml depending on the fruit.
• YieldThe original claims ten servings, which works out at one whole egg per person.