coat a spoon
A cooking technique used to test the doneness of cooked, egg-based custards and sauces. The mixture is done when it leaves an even film (thin to thick, depending on the recipe instructions) on the spoon. This film can be tested by drawing your finger across the coating on the spoon. If it doesn't run and leaves a clear path, it's ready.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.