15 lasagna noodles
7 tablespoons olive oil, divided
2 medium-large onions, halved and thinly sliced (4 heaping cups)
Ground black pepper
1 teaspoon dried thyme leaves, divided
2 pounds baby bella mushrooms, cleaned and sliced
8 garlic cloves, minced
2½ cups milk
1½ cups vegetable broth
½ ounce dried mushrooms, finely chopped
½ pound grated provolone cheese (2½ cups)
1¼ cup grated Parmesan cheese
5 tablespoons flour

Bring 3 quarts of water and 1 tablespoon of salt to boil a large pot. Add lasagna noodles and, using back-of-the-box cooking times as a guide, cook, stirring frequently at first to prevent sticking, until noodles are just tender. Drain noodles, laying them out in a single layer to prevent sticking. Meanwhile, heat 2 tablespoons of the oil over medium-high heat in a large skillet. Add onions and sauté until golden brown, about 10 minutes. Reduce heat to low, and continue to cook until onions are caramel brown, seasoning lightly with salt and pepper and ½ teaspoon of the thyme, about 10 minutes longer. Transfer to a bowl and set aside. Return skillet to burner and heat another 2 tablespoons of oil. Add mushrooms and sauté until all of their liquid evaporates and mushrooms start to turn golden, lightly seasoning with salt, pepper, 2 of the garlic cloves and remaining ½ teaspoon thyme towards the end of cooking, 10 to 12 minutes. Remove mushrooms from heat and set aside. Microwave milk, broth, and dried mushrooms in a microwave-safe bowl until liquid is steamy hot and mushrooms are soft, about 5 minutes. Heat remaining 3 tablespoons of oil and remaining 6 garlic cloves over medium-high heat in a large saucepan or small Dutch oven. When garlic starts to sizzle and turn golden, whisk in flour until smooth, and then vigorously whisk in milk mixture and heat until sauce starts to bubble and thicken. Stir in Parmesan and season to taste with salt and pepper. Remove from heat, place plastic wrap directly over the sauce’s surface to keep a skin from forming. Adjust oven rack to upper middle position and heat oven to 425 degrees. Smear ¼ cup of the sauce over bottom of baking dish. Assemble the next 4 layers in the following order: 3 noodles, â…” cup sauce, ¼ of the onions, ¼ of the mushrooms, ½ cup provolone, and 2 tablespoons Parmesan. Assemble final layer with remaining noodles, sauce and cheeses. Seal lasagna with foil and bake until bubbly, about 35 minutes. Remove foil, and then broil until cheese is spotty brown, 5 to 7 minutes longer. Let stand 10 to 15 minutes. Cut and serve