Serves 6 as a main course
8 as a side
Roasting mushrooms to concentrate their flavour and then adding a few flame cooked ones gives this vegetarian gratin wonderful complexity. This is a good recipe to use for distinctively shaped and flavoured mushrooms like chanterelles or oyster mushrooms as they will retain many of their unique characteristics, but any variety will work excellently.
2 pounds assorted mushrooms such as cremini, oyster, chanterelle or white button
1 tablespoon extra-virgin olive oil, plus more for the baking dish
3/4 teaspoon fine sea salt
4 ounces shredded Gruyère cheese, divided
1/4 teaspoon ground black pepper
1/4 teaspoon grated nutmeg
2 tablespoons chopped fresh parsley
1/3 cup whole wheat bread crumbs
Preheat the oven to 375°F.
Halve or thickly slice mushrooms that are larger than about 1 1/2 inches across; leave the rest whole. Set 6 whole mushrooms aside. Place remaining mushrooms on a large rimmed baking sheet and toss with oil and 1/2 teaspoon of the salt. Roast until very soft and browned, about 35 minutes.
Meanwhile, skewer reserved mushrooms on 2 metal skewers. Hold the ends of the skewers with oven mitts and place mushrooms over an open flame (such as a gas burner or outdoor grill on high setting) and cook, turning frequently, until charred all over, 3 to 4 minutes. Remove mushrooms from the skewer and place on a cutting board. When cool enough to handle, coarsely chop.
Oil a 1 1/2-quart gratin dish or 8-inch-square baking dish. In a large bowl, stir together half-and-half, half of the cheese, pepper, nutmeg and remaining 1/4 teaspoon salt. Stir in roasted mushrooms and charred mushrooms. Pour mixture into a gratin dish and press down gently with the back of a spoon to level. Sprinkle with remaining cheese, parsley and bread crumbs. Lower the oven temperature to 350°F; bake gratin until top is well-browned and edges are bubbling, about 40 minutes. Cool 10 minutes before serving.