This rich vegetarian casserole is perfect for main-course status at the holiday table. Any deep casserole or baking dish with a 5-quart capacity will work for cooking.
The polenta can be cooked, cooled, covered tightly and refrigerated for up to 1 week. The squash and the mushrooms can be roasted and refrigerated for up to 5 days. The tomato sauce can be made and refrigerated for up to 1 week. The entire casserole can be assembled up to 3 days in advance and refrigerated. Bring to room temperature before baking; if you must bake it cold, be sure to allow more oven time.
POLENTA STUFFED WITH SQUASH AND MUSHROOMS
16 to 20 servings
12 cups water, plus more for moistening the bowl
1 tablespoon sea salt, plus more to taste
3 cups coarsely ground polenta
One 2 1/2-to-3-pound squash, such as butternut, acorn, buttercup or other winter squash, peeled, seeded and cut into 1/2-inch cubes
1/4 cup extra-virgin olive oil
1 1/2 pounds mixed mushrooms, such as oyster, cremini and shiitake, cleaned, stemmed and cut into large pieces
1 teaspoon dried thyme
14 1/2 ounces canned, no-salt-added crushed tomatoes, plus their juices
1 1/2 ounces Parmigiano-Reggiano cheese, finely grated
8 ounces smoked mozzarella, grated
Bring the water to a boil in a large pot over medium-high heat. Add 1 tablespoon of the salt and gradually whisk in the polenta, 1/4 cup or so at a time. Reduce the heat so the water is at a gentle boil, lightly bubbling all around but not rolling, then cover and cook for 10 minutes. Uncover and stir vigorously for 1 minute, then cover and cook for 10 minutes. Repeat two more times, until the polenta has been cooking for a total of about 40 minutes, then uncover and cook for 5 minutes to make sure no grainy texture remains. Remove from the heat.
Moisten a large mixing bowl with a little water, then pour in the hot polenta to cool.
Preheat the oven to 400 degrees.
While the polenta is cooking, toss the squash on a large rimmed baking sheet (or two, if needed to keep the squash from overlapping) with one tablespoon of the oil; season with salt to taste. Toss the mushrooms on one or two separate large rimmed baking sheets with 1 tablespoon of the oil, the thyme and salt to taste.
Roast the mushrooms until they collapse, exude liquid and start to lightly brown, about 10 minutes. Roast the squash until it is browning on the bottom and fork-tender, about 20 minutes. Cool those ingredients.
Pour the tomatoes and their juices into a narrow, deep bowl. Add 1 tablespoon of the oil, then use an immersion (stick) blender to puree until smooth. Season with salt to taste.
Lightly grease the large casserole dish with the remaining 1 tablespoon of oil. Spread half of the polenta in the bottom of the dish, using your hands to break it up and spread it around if it has firmed up in cooling. Evenly sprinkle half of the Parmigiano-Reggiano cheese on the polenta, then layer on the squash cubes, half of the mozzarella and all of the mushrooms. Top with the remaining polenta, spreading it as evenly as you can on top of the mushrooms. Pour the pureed tomatoes on top, leaving an inch or so of the polenta exposed around the edges, then scatter the remaining mozzarella and Parmigiano-Reggiano cheese on top.
Bake until the cheese has melted and started to brown and the filling is bubbling around the edges of the casserole, about 30 minutes. Cool slightly before cutting into squares or wedges. Serve warm.
Nutrition per serving (based on 20): 190 calories, 7 g protein, 27 g carbohydrates, 6 g fat, 3 g saturated fat, 10 mg cholesterol, 430 mg sodium, 2 g dietary fiber, 3 g sugar