Cook noodles until al dente. Drain and set aside.

Preheat oven to 350F. Spray a 13x9-inch baking dish with cooking spray.

In a saucepan, melt butter.

Cook the onions and mushrooms until tender, approximately 3-5 minutes.

Mix in flour and cook for one minute. Slowly whisk in the beef broth and Worcestershire sauce. Heat to simmer and cook until thickened.

Reduce heat to low and add heavy cream and sour milk. Season the dish with salt and pepper.

Add the noodles, sauce, and meatballs to a prepared baking dish. Bake for 20-30 minutes, or until sauce has thickened and bubbling.

If desired, garnish with fresh chopped parsley.