- 1/4 cup (1/2 stick) unsalted butter
- 2 1/2 cups chopped onions
- 1/2 pound mixed crimini and oyster mushrooms, sliced (about 3 cups)
- 1 pounds white scallop or other summer squash, grated
- 1/2 c vegetable or chicken stock
- 4 cups basic tomato sauce
- 4 tablespoons chopped fresh thyme, divided
- 4 tablespoons sliced fresh sage, divided
- 3 15-ounce containers whole-milk ricotta cheese
- 4 cups grated mozzarella cheese, divided
- 2 cups grated Parmesan cheese, divided
- 4 large eggs
- Olive oil
- 1 9-ounce package no-boil lasagna noodles
Melt butter in large skillet over medium-high heat. Add onions; sauté until soft, about 8 minutes. Increase heat to high; add mushrooms and cook until tender, stirring constantly, about 3 minutes. Season with salt and pepper. Transfer mushroom mixture to bowl; set aside.
Add squash, broth, 3 tablespoons thyme, and 3 tablespoons sage to same skillet. Cover and simmer over medium heat until squash is just tender, about 6 minutes. Uncover and cook until squash is very soft but still retains shape, about 5 minutes. Season with salt and pepper and stir into tomato sauce.
Mix ricotta, 2 cups mozzarella cheese, 1 1/2 cups Parmesan cheese, and remaining 1 tablespoon thyme and 1 tablespoon sage in large bowl. Season to taste with salt and pepper; mix in eggs.
Brush 13x9x2-inch glass or ceramic baking dish with oil. Spread 1 cup ricotta mixture over bottom. Arrange 3 noodles on top. Spread 13/4 cups ricotta mixture over noodles. Arrange 1 1/3 cups squash mixture over. Sprinkle with 1/2 cup mushrooms and 1 cup mozzarella. Top with 3 noodles, then 1 3/4 cups ricotta mixture, half of remaining squash, 1/2 cup mushrooms, and remaining 1 cup mozzarella. Repeat with noodles, 1 3/4 cups ricotta mixture, remaining squash, and remaining mushrooms. Top with 3 noodles. Spread remaining ricotta mixture over; sprinkle with remaining Parmesan. Cover with oiled foil.
Preheat oven to 350°F. Bake lasagna, covered, 35 minutes. Uncover; bake until heated through, about 25 minutes longer. Let stand 10 minutes before serving. (The lasagna can be assembled one day ahead and refrigerated.)