YUMMY SUMMER VEGGIE GRATIN
Water is the enemy of your gratin, and cooking method must be approached ruthlessly
A gratin of summer vegetables should be the easiest thing in the world to make in August: a no-recipe breeze for the carefree summer cook.
Slice up squash, tomatoes, etc.; arrange attractively; bake.
But this sunny, soap-commercial method has never worked for me. My gratins are often swamped with tomato water, filled with slices of raw onions and overcooked zucchini, and topped with a pale, dusty desert of bread crumbs.
This summer, I set out to solve all of the problems, feeling my way to a not-soggy, crisp-topped, satisfying gratin.
When zucchini and tomatoes are plentiful (read: overwhelming), it is tempting to pile lots and lots of them into a gratin. But part of what makes these summer vegetables fresh and delicious is that they are full of water. That water is the enemy of your gratin, and must be approached ruthlessly. (Winter vegetables, like potatoes, pumpkins and parsnips, have less water and more starch, and make beautiful gratins.)
The simplest way to get rid of water is to apply heat. And so it’s a good idea to cook some or all of the ingredients before they ever see the inside of the baking dish. Cooking is the most efficient way to evaporate all that water in vegetables, and has a side benefit of concentrating their flavours.
Fortunately, the cooking can happen any way you like. You can sauté or broil or grill the vegetables. In fact, you can cook some of them and leave others raw; for example, as in the recipe here, if you cook the tomatoes, you can leave the squash alone. Since the casserole is baked uncovered and at a high temperature, water will also evaporate in the oven.
Here are some universal tips for achieving a crusty, caramelized gratin:
Do not crowd the pan. It is tempting to jumble three pounds of raw zucchini and tomatoes into a baking dish, but that way lies sogginess. The vegetables should overlap, but not as closely as fish scales. They should look more like roof shingles, with plenty of exposure to air. If you are determined to bake a large quantity, use two pans, or cook all the vegetables first.
A baking dish is pretty, but a heavy heathugging skillet is better at cooking the vegetables from below.
Any uncooked ingredients should be slicked with oil before arriving in the oven. Oil conducts heat and will prevent the slices from sticking together, allowing hot air to circulate.
Never cover a gratin containing raw vegetables while baking. This creates a steam bath inside the dish.
Provence is the natural habitat of the summer vegetable gratin (or, as it is called there, a tian), so for further improvements I went to the source. In her classic 1976 cookbook “The Cuisine of the Sun,” about the cooking of the French Riviera, the author (and Nice native) Mireille Johnston wrote that tomatoes that are to be baked should be cooked before going into the oven.
Fry them gently until “all their excess water is cooked away and they look transparent — like candied fruit,” she wrote. “In Provence, they say that they must look like a vitrail — a stained-glass window.” And indeed, they do. (A more time-saving way to incorporate tomato flavour in a gratin is to use a thick tomato sauce to coat the bottom of the pan.)
Traditional Provençal tians are topped not with cheese but with bread crumbs. But bread crumbs are not always the dry, microscopic shards familiar to us from cardboard tubes.
“They are a terribly misunderstood ingredient,” said Jane Sigal, a writer who worked in Provence in the 1980s as a kitchen assistant to Julia Child’s coauthor (and sometime frenemy) Simone Beck.
Although the distinction has mostly been lost in traditional cooking, she said, there are two distinct kinds of bread crumbs: dry and soft.
Dry bread crumbs are the familiar sandy style made from stale bread, and are good for coating food that’s to be fried. (Panko crumbs, made from Japanese-style white bread, are even better.)
But fresh bread crumbs are semi-soft bits of fluff, ranging in size from a kernel of popcorn to a fully popped piece. They have taste and a bit of chew, are made from bread that is no more than one day old, and are precisely what you want for a bread crumb topping. Dry bread crumbs will never bake into a real crust, but fresh bread crumbs will — as long as richer ingredients are added with a generous hand.
“If there’s one thing people can do to improve their crusts, it’s to add olive oil,” Sigal said.
The bread crumbs should be thoroughly moist, with an oily sheen. Cheese is optional but helps the crust form. For extra frills and flavours, you might add minced garlic and parsley to the bread crumbs, producing the classic Provençal topping for baked tomatoes.
Summer vegetable gratin with squash and zucchini slices atop a base of onion and bell pepper, which can optionally be topped with a layer of tomatoes, cheese and bread crumbs, as shown below. There are some tricks, however, to getting it right and avoiding a mushy mess.