Heat oven to 375 degrees. Lightly spray a 9x13-inch baking dish with cooking spray. Cook noodles according to package directions, using minimum cooking time. Drain and set aside.

In a large skillet, melt butter over medium heat. Add mushrooms and onion and cook until just tender, 3-5 minutes. Stir flour into mushroom and onion mixture. Gradually stir in beef broth and bring to a simmer until mixture begins to thicken. Stir in Worcestershire sauce and salt and pepper, to taste.

Cook for an additional 3-5 minutes. Add cream cheese, stirring constantly with whisk until cream cheese is mostly incorporated (small pieces of cream cheese may remain but will incorporate in baking). Remove from heat and stir in whipping cream.

Stir in cooked noodles and meatballs, carefully mixing to coat. Cover and bake 30 to 35 minutes or until sauce is bubbling and casserole is heated through. Let stand for 10 minutes. Stir before serving, and garnish with fresh parsley, if desired.