Preheat the Oven – Set the oven rack to the middle position and the temperature to 375°F (190ºC).
Cook the Pasta – In a large Dutch oven or pot, bring water to a boil. Add 1 tablespoon of salt and stir to dissolve. Add the spaghetti and cook according to package directions until al dente, about 9 to 10 minutes.Drain in a colander and rinse with cool water for about 30 seconds to immediately stop the cooking process. Separate them with a spoon so they do not stick together. Leave some moisture on the surface and set it aside.
Cook the Vegetables – Heat a large pot over medium heat. Melt 2 tablespoons butter, then add the onions. Saute until fragrant and translucent, about 3 minutes. Add the garlic and Italian seasonings, and saute for 30 seconds.Add the mushrooms, 1 teaspoon salt, and pepper. Cook until most of the moisture is released and mushrooms are tender, about 5 to 6 minutes. Transfer to a bowl and set aside.
Make the Sauce – Melt 6 tablespoons of butter in the pan. Stir in the flour, and cook until the roux turns golden blonde in color, about 2 minutes. Turn the heat up to medium-high. Gradually whisk in the chicken stock, stirring constantly until thickened. Stir in the heavy cream, whisking until a smooth sauce is formed.Turn off the heat. Stir in 1/2 cup of the mozzarella and 1/2 cup of parmesan cheese until melted. Stir in 1 teaspoon of salt. Season the sauce to taste with more salt and pepper if desired.
Combine Ingredients – Add the pasta, turkey, peas, and mushrooms to the pot. Stir to combine.
Layer the Casserole – Lightly grease a 13 x 9-inch baking dish with olive oil or butter. Spread the pasta mixture evenly in the pan. Evenly sprinkle 1/2 cup mozzarella cheese, 1/2 cup parmesan cheese, and bread crumbs on top.
Bake – Bake until the edges are hot and bubbly and the surface is lightly golden brown, 30 to 35 minutes. For an extra crispy and golden brown surface, broil for 2 to 3 minutes. Watch carefully for the color change to prevent burning.
Serve – Garnish with some of the chopped parsley and serve hot.
Notes
Recipe Yield: 16 cups
Serving Size: 2 cups
Storing: Cool and store in an airtight container for up to 3 days. Place in a resealable bag for up to 1 month, and defrost before using.
Reheat: Cover and microwave on high for 15 to 30 seconds, stirring in between, until hot. If needed, add a small amount of water to make the sauce creamy.