Nappé

As such “nappé” is a conservative culinary term used to describe the proper thickness of sauce; the thickness being so that the sauce will coat the back of a spoon. Another method to determine if the liquid has reached the proper thickness is to draw a spoon through the sauce, it should come together after a moments pause (this is, of course, in the pan and the sauce is about a centimeter in depth).

I say conservative since in modern American cooking (and quite possibly others) there is seen a great divergence from the old standards in French sauce making. Much thinner sauces are often used and deemed acceptable. There is a trend to make sauces without a starch thickener; such as reductions, broths and purées.

I am unsure if the term is actually used in modern French kitchens; I see no entry for the word in Larousse Gastronomique or in La Varenne Pratique. Nor after a cursory glance through the sauce entry of Larousse (which is extensive being around a dozen pages) did I see any use of the word.

My culinary arts text book defines nappé as such: (1) the consistency of a liquid, usually a sauce, that will coat the back of a spoon; (2) to coat food with a sauce.

Verily in French the word means tablecloth or a cover.