01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish.
02 - Boil salted water and cook pasta until al dente. Drain and set aside.
03 - In a large skillet, melt butter over medium heat. Add onions and mushrooms, cooking until mushrooms brown and onions soften, about 7 minutes.
04 - Stir in minced garlic and cook for 1 minute. Sprinkle flour over mixture and cook while stirring for 2 minutes.
05 - Gradually whisk in white wine if using, then chicken broth, whole milk, and heavy cream. Stir continuously until thickened, about 3 to 5 minutes.
06 - Add dried thyme, nutmeg, salt, and pepper. Remove from heat and stir in Parmesan, mozzarella or Swiss cheese, cooked turkey, and peas if using.
07 - Mix sauce evenly with cooked pasta and transfer to prepared baking dish.
08 - In a small bowl, combine breadcrumbs with 1 tablespoon melted butter and extra Parmesan. Sprinkle evenly over pasta mixture.
09 - Bake uncovered for 25 to 30 minutes, until bubbly and golden on top.
10 - Allow to rest for 10 minutes before serving to set.