Pre-heat oven to 425 degrees.
Cook pasta and set aside.
In a dutch oven, over medium heat, add oil and 2 tablespoons of butter, and cook chicken until cooked through and browned. Remove chicken from the dutch oven and set aside.
Add 2 more tablespoons of butter and mushrooms to dutch oven and cook until browned and water has evaporated, about 10-15 min. Add onions and sauté until onions are translucent. Add garlic and cook for 1 minute. Remove from dutch oven and place in the bowl with the chicken.
Add remaining butter and flour to the dutch oven. Cook for 1-2 minutes. Add white wine and cook until thickens. Whisk in milk, cream, broth, nutmeg, salt and pepper. Cook until sauce thickens, about 10 minutes.
Add chicken, mushrooms-onions, pasta and ½ cup Parmesan cheese and parsley together to dutch oven and mix until well combined.
Put into a buttered 9 by 13-inch casserole pan.
Cover with breadcrumbs and remaining Parmesan cheese.
Bake for 25-35 min or until golden brown and bubbly.