Zucchini and Tomato Gratin

The secret to making this gratin especially tasty is to sauté the zucchini ahead of time, to evaporate the water they contain and to concentrate their flavor. If you can’t find fresh marjoram, thyme will do, but marjoram is marvelous and worth the search. If you can’t find good, ripe fresh tomatoes, you can use canned (see Linguine with Tomato Sauce head-note).