Mousseline Sauce

Sauce Mousseline (a warm butter emulsion lightened with whipped cream) teaches one true thing: the air goes in last, and the heat does not come back. Stiffly whipped cream gives Mousseline its pale color and soft, billowing body, but only while the Hollandaise is warm rather than hot and the finished sauce goes directly to the table.

The original assumed a saucier with Hollandaise waiting at a tepid corner of the range, a tammy already used, and cream whipped for the instant of service. At home, the finished Hollandaise Sauce (No. 30), a cold bowl, a thermometer, and a flexible spatula do the same work. The holding station is brigade scaffolding and goes; the last-minute fold is the dish and stays. Its exact ratio remains untouched: two volumes Hollandaise to one volume stiffly whipped cream, converted here into one generous two-quart dinner-party batch. One cook, one stove, one evening.

Lighten the Hollandaise first with a smaller portion of cream, then fold in the rest with broad, patient strokes. This equalizes the two mixtures without beating out all the air. That first addition is the step that decides the sauce, so make it gently and keep the rescue water close. Ça se rattrape.