• Preheat oven to 375 degrees.

To make the noodles:

• In a large stock pot, bring 4 quarts water and 1 tablespoon salt to boil. Add noodles and cook until just al dente, about 10 minutes. Drain well and rinse with cold water to prevent sticking.

To make the sauce:

• Meanwhile, in a large saucepan or Dutch oven over medium-high heat, heat olive oil until shimmering. Add mushrooms, onions, and 1/2 teaspoon salt and cook until the mushrooms have released most of their liquid, about 10 minutes. Stir in garlic until fragrant, about 30 seconds.
• Stir in spinach, crushed tomatoes, tomato sauce, sugar, basil, Italian seasoning, and fennel seeds. Simmer uncovered for 15 minutes, stirring occasionally. Season to taste with salt and pepper (I like 1 1/2 teaspoons salt and 1/2 teaspoon pepper). You should have about 2 quarts sauce.

To make the cheese filling:

• Meanwhile, in a large bowl, combine ricotta cheese with egg, parsley, and salt. Chill until the sauce is finished.

To assemble the lasagna:

• In the bottom of a 9-inch x 13-inch baking dish, spread 2 cups sauce. Arrange a single layer of uncooked noodles over the meat sauce (I do 3 full-size noodles lengthwise and then a partial noodle crosswise). Spread with a heaping 2/3 cup of the ricotta mixture. Top with about 1 1/2 cups (5 ounces) of mozzarella. Sprinkle with 1/3 cup Parmesan cheese.
• Spoon 2 cups sauce over the cheese. Make another layer of noodles, ricotta mixture (heaping 2/3 cup), mozzarella (1 1/2 cups) and Parmesan (1/3 cup). Repeat layers 1 more time, for a total of 3 layers.
• Spray a large piece of foil with nonstick spray and cover baking dish. Bake 15 minutes. Remove foil and bake an additional 25 minutes, or until hot and bubbly. Cool at least 10 minutes before serving.