This cold sauce—it’s more like a relish, really—takes you just a short step away from eating raw oysters with nothing at all on them. The flavors of the sauce don’t get in the way of the oyster, and the contrast between the metallic brininess and softness of the oyster and the acidity and crunch of the sauce is very pleasant. Don’t chop the shallots in a food processor; dice them with a sharp knife.