1 package lasagna noodles, cooked and drained
8 tablespoons butter or margarine
½ onion, chopped
1 carrot, peeled and chopped
½ cup flour
5 cups milk
1 teaspoon nutmeg
Salt and pepper
4 tablespoons butter or margarine
4 tablespoons olive oil
4 (8 ounce) packages sliced mushrooms
2 teaspoons minced garlic
1 tablespoon tomato paste
1 (29 ounce) can diced tomatoes, drained
3 cups grated mozzarella cheese

Make béchamel sauce:

Heat the 8 tablespoons butter or margarine in a saucepan over medium heat. Add onion and carrots and cook for 5 minutes. Whisk in flour and cook for 2 minutes. Whisk in milk. Bring to a boil; reduce and heat and simmer, continually whisking, 25 minutes. Sauce should thicken. Stir in nutmeg, salt and pepper.

In the meantime, heat 4 tablespoons butter or margarine and olive oil in a large skillet over medium heat. Add mushrooms and garlic and sauté for about 10 minutes. Stir in tomato paste and diced tomatoes and cook for 10 minutes, stirring occasionally. Set aside.

Preheat oven to 375 degrees. In a 9 x 13-inch baking dish spread a layer of tomato-mushroom sauce. Cover with a layer of noodles. Spread 1 cup of béchamel sauce over top. Sprinkle with 1 cup of cheese and 2 cups of tomato-mushroom sauce. Add another layer of noodles and repeat. Top with remaining noodles and remaining 1 cup cheese. Bake for about 45 minutes to 1 hour until cheese is lightly browned.