Preheat your oven to 375°F. Cook the pasta according to package directions until al dente, drain well, and set aside.
In a large skillet over medium-high heat, melt 3 tablespoons butter. Add the mushrooms and cook until golden brown, about 5-6 minutes. Add the onion and cook for another 3 minutes until softened, then stir in the garlic and cook for 30 seconds.
Sprinkle the flour over the vegetables and stir constantly for 1 minute to cook out the raw flour taste.
Slowly pour in the chicken broth and wine, whisking constantly to prevent lumps. Bring to a simmer and cook for 3-4 minutes until slightly thickened.
Reduce heat to medium-low and stir in the heavy cream, 1 cup of Parmesan cheese, thyme, salt, and pepper. Let the sauce simmer gently for 2-3 minutes until smooth and creamy.
Add the cooked pasta and turkey to the sauce, tossing everything together until well coated. Transfer the mixture to a greased 9x13-inch baking dish.
In a small bowl, mix together the mozzarella cheese, remaining 1/2 cup Parmesan, and panko breadcrumbs. Sprinkle this mixture evenly over the top of the casserole and dot with the remaining 1 tablespoon of butter.
Bake for 25-30 minutes until the top is golden brown and bubbly. Let cool for 5 minutes, garnish with fresh parsley, and serve hot.
