Preheat oven to 350 degrees. Grease a 9x13 inch baking dish.
In a medium bowl, toss together the ingredients for the topping; set aside.
For the casserole, cook noodles in boiling, salted water for 1-2 minutes. rinse with cold water and drain.
In a large saute pan or Dutch oven, melt 4 tablespoons butter. Add onion and garlic and saute until soft and fragrant, 3-5 minutes. Stir in flour and ranch seasoning and cook a few minutes longer.
Whisk in broth and half and half. Bring to a boil and simmer until thickened. Reduce heat and stir in cream cheese. Cook and stir until cream cheese is melted.
Stir in noodles, chicken, shredded cheese and parsley. Season with salt and pepper, to taste. Transfer noodle mixture to the prepared pan.
Sprinkle topping over casserole. Bake, uncovered, until golden and bubbly, 25-30 minutes.