Easy Vegetarian Lasagna

Name: Easy Vegetarian Lasagna
Ingredients: 2 tablespoons unsalted butter; 1 to 2 large shallots, thinly sliced (about 3/4 cup); 10 ounces fresh mushrooms, such as shiitakes or buttons, chopped (about 3 cups); 1 pound frozen kale or spinach, thawed; Kosher salt and freshly ground black pepper; One 9-ounce box no-boil lasagna noodles, broken into 2-to-3-inch pieces; 2 cups heavy cream; 4 cups part-skim ricotta cheese; 1/2 cup grated Parmesan; 1/2 teaspoon ground nutmeg; 1 cup shredded mozzarella; 1/8 teaspoon red pepper flakes