Mustard Sauce with Cream

Sauce Moutarde à la Crème (mustard sauce with cream) teaches a small but essential law of cold sauces: season the concentrated base before you dilute it. Salt, pepper, and lemon disappear into the smooth mustard; once the cream enters, you are controlling body. The finished sauce should be pale ivory with an ochre cast, gently sharp, and loose enough to cloak celery without running away.

The original formula is a service instruction: three spoonfuls of mustard, then the “necessary quantity” of cream, because a garde-manger (cold-table cook) mixed by sight for several plates. It required neither a stockpot kept on the fire nor a salamander, and its only brigade scaffolding was quantity. For one cook, I have divided the mustard by three and given the cream as a narrow range, enough for four generous portions. One cook, one stove, one evening.

Adding the cream little by little is not scaffolding. It is the dish. Start with very fresh cold cream and stop when the sauce falls from the spoon in a broad ribbon; that gradual loosening is the one step that matters.