Chicken, Spinach, and Mushroom Lasagna

Simmer the chicken thighs until tender in the broth, which will become the basis for the creamy bechamel sauce. Noodles without boiling absorb more liquid during baking, after freezing and reheating the slices are dense.
In a large saucepan over medium-high heat, bring the broth to a boil. Add the chicken; reduce the heat and simmer for 18-20 minutes or until the chicken is tender. Remove the chicken from the pan; leave the broth. When it is cool enough, chop it with 2 forks.Preheat a large skillet over medium-high heat. Add the butter; stir to coat. Add the onion, garlic, 1/2 teaspoon salt, thyme, pepper, and mushrooms; simmer for 8 minutes. Add the spinach 1 pack at a time, cook for 2 minutes after each addition or until the spinach wilts before adding more. Remove the pan from the heat; add the chicken.Preheat the oven to 375 degrees.Brush 2 8-inch square baking pans with cooking spray. Combine the milk, flour and nutmeg, stirring with a whisk, until smooth. Bring the remaining broth to a boil over medium-high heat. Gradually add the milk mixture to the stock mixture, stirring constantly with a whisk. Add the remaining 1 teaspoon of salt. Cook for 5 minutes or until thickened, stirring occasionally. Remove the pan from the heat; add the parmesan Reggiano. Pour 1/2 cup of the sauce over the bottom of each baking dish. Top each with 2 noodles, 1 1/2 cups chicken mixture, 3/4 cup sauce, and 1/4 cup mozzarella, making sure the noodles are covered with the sauce. Repeat the layers once with the noodles, chicken mixture and sauce. Sprinkle evenly with the remaining 4 noodles, 1/2 cup remaining sauce, and 3/4 cup mozzarella.Cover the dishes tightly with foil smeared with cooking spray. Bake at 375 degrees for 25 minutes. Remove and bake at 375 ° C for 10-15 minutes or until it is browned and bubbling, or follow the freezing instructions. Let stand for 5 minutes before serving.Freezing method: Allow the pan to cool completely. Cover with foil; freeze for up to 2 months. Defrost: In a metal pan: Defrost overnight in the refrigerator. In glass or ceramic dishes: Remove the lid and reheat in the microwave on high power for 15 minutes or until defrosted. Preheat: Cover; bake at 375 ° C for 25 minutes. Uncover and bake for 5 minutes.