Preheat oven to 375 degrees. Butter a casserole dish and set aside.
Bring the chicken stock and water to a boil. Reduce to simmer, add egg noodles, and cook according to package directions until tender. Drain most of liquid (leave about 1/2 cup in with the noodles). Cover and set aside.
In a large, non-stick skillet over medium-high heat, add the olive oil and 2 tablespoons of butter to melt.
Add the onions and mushrooms and cook until browned, about 8-10 minutes. Add the chicken, salt and pepper and stir to combine.
Add the Marsala wine and allow to simmer for 5 minutes.
Whisk together the cornstarch and one tablespoon of water and stir into the chicken Marsala mixture.
Add the chicken Marsala mixture to the cooked noodles.
Add the sour cream and stir until completely combined.
Spread the casserole evenly into the dish.
Microwave the remaining tablespoon of butter. Stir the melted butter into the Panko bread crumbs. Add the parsley and stir to combine.
Top the casserole with bread crumb mixture. Bake the casserole for 20 minutes. Serve immediately.