Recipe: How to Make a Vegetable Gratin

How to Make a Vegetable Gratin

A gratin is a great way to bind ingredients together and cook them under what becomes a crisp, golden brown crust. I bake root vegetables in a mixture of grated cheese, cream, and milk that reduces over the vegetables to make a thick rich sauce. Potatoes are particularly marvelous in this style of gratin, because they're such wonderful foils for cream and cheese, and their starchiness thickens the sauce. Turnips and celery root are good in combination with potatoes, because the potatoes add starch, which helps hold the gratin together, and softens the aggressive taste of the other vegetables. Parsnips can be used on their own, because they have a high starch content and their flavor is milder than turnip and celery root.

Because watery vegetables such as zucchini, summer squash, eggplant, and mushrooms contain so much liquid of their own, their moisture should be cooked out to concentrate their flavor. In the zucchini gratin, the zucchini are first sautéed and then layered with a fairly thick tomato sauce (coulis) and cheese.

Kitchen Notes and Tips

When making a root vegetable gratin, add just enough liquid so that all but the topmost layer is covered and when you press down on it, the liquid oozes up around and barely covers the top layer. The proportion of cream to milk is up to you. Using very little cream, however, increases the possibility that the milk will curdle and give the gratin a grainy texture. A proportion of half cream and half milk makes the gratin creamy but not too rich. For a completely lean gratin, use broth instead of milk or cream.

The thinner and wider the gratin, the greater the proportion of caramelized, crispy crust (which is, remember, the whole point).
The moister the vegetable, the thinner the gratin should be, so the moisture in ingredients like zucchini will evaporate and the vegetable's flavor will be concentrated. Root vegetable gratins can be somewhat thicker. In general, a gratin should be about 1 to 2 inches deep before it is cooked.
Bake gratins at 375 degrees F.
The gratin is done when it is no longer soupy and the surface is browned and caramelized. Monitor the heat to make sure the gratin is cooking evenly: If the top browns too fast, turn the oven down. If the liquid isn't bubbling or the vegetables are sitting in a puddle of their own juices, turn the oven up.

Buy the Book!

Essentials of Cooking
By James Peterson
Artisan, December 1999
Hardcover, $40.00
300 pages, more than 1100 photographs
ISBN: 1-57965-120-8
Recipe reprinted by permission.