Serve with a green salad and some beans, tofu or other protein of your choice.
1 tablespoon olive oil, plus more for the baking dish
1 large yellow or white onion, thinly sliced (about 2 cups)
1 red bell pepper, seeded and finely chopped (about 1½ cups)
1 pound button or cremini mushrooms, trimmed and sliced (heaping 4 cups)
¼ teaspoon dried thyme
1½ teaspoons kosher salt
½ teaspoon freshly ground black pepper
3 pounds Yukon Gold or russet potatoes, peeled and each cut in half lengthwise
2 tablespoons flour
1½ cups grated Gruyère cheese (about 6 ounces)
1½ cups store-bought mushroom broth (see note)
Preheat the oven to 400 degrees. Lightly grease a 9-by-13-inch baking dish with a little oil (or coat it with cooking oil spray).
Heat the tablespoon of oil in a large pot over medium-high heat. Once the oil shimmers, stir in the onion and red bell pepper; cook, stirring frequently, until the onion starts to become translucent, 5 to 6 minutes. Stir in the trimmed mushrooms, thyme, salt and black pepper; cook until the mushrooms have browned and cooked down a bit, 2 to 3 minutes. Turn off the heat.
Cut the potato halves crosswise as thinly as you can (into half moons, no thicker than ¼ inch). The yield should be about 6 cups. Layer half the sliced potatoes in the baking dish and then sprinkle evenly with 1 tablespoon of the flour. Spread the mushroom-bell pepper mixture over the potatoes, then scatter one-third of the grated Gruyere over that layer. Use the remaining potato slices to build the next layer, then sprinkle with the remaining tablespoon of flour. Pour the mushroom broth over everything and top with the rest of the cheese.
Cover tightly with aluminum foil; bake (middle rack) for 30 minutes, then uncover and bake until the potatoes are tender and the top is crusty and golden brown, another 30 minutes. Let stand for at least 10 minutes before serving.
Note: If you can't find commercially prepared mushroom broth (typically in aseptic quart boxes), pour 2½ cups boiling water over ½ cup dried sliced mushrooms, such as shiitake, and let them soak for at least 20 minutes. Strain through a fine-mesh sieve into a large liquid measuring cup. (You'll have more than you need for this recipe, but it can be refrigerated for up to 2 weeks or frozen for up to 3 months.) The soaked dried mushrooms can be rinsed, sliced and added to the fresh mushrooms in this dish.
Nutrition | Per serving: 270 calories, 11 g protein, 36 g carbohydrates, 9 g fat, 5 g saturated fat, 25 mg cholesterol, 450 mg sodium, 1 g dietary fiber, 2 g sugars
Adapted from "The Moosewood Restaurant Table: 250 Brand-New Recipes from the Natural Foods Restaurant That Revolutionized Eating in America," by The Moosewood Collective (St. Martin's Griffin, 2017).