Preheat oven to 350 degrees.
In a large skillet set over medium heat, add the butter. Once melted, add the mushrooms and cook until browned, about 5 minutes. Add the shallot and cook until translucent, about 2 minutes.
Whisk in the flour and cook until it turns a pale gold color, about 1 minute. Slowly pour in the chicken broth, whisking to scrape up any browned bits at the bottom of the pan, and to prevent lumps from forming. Bring the heat up just a little. Continue whisking while pouring in the cream, then the sour cream and seasonings. Let the mixture simmer for 5 minutes.
Remove from the heat and whisk in the cheeses. Add the chicken and cooked noodles, mix to combine.
In a small microwave-safe bowl, melt the butter for the topping. Toss in the breadcrumbs along with the garlic powder, paprika, and salt. Once combined, sprinkle over the noodles and bake, uncovered for 30 minutes. Turn oven onto broil for extra golden brown breadcrumbs during the final few minutes.
Remove from the oven and let stand for 10 minutes before garnishing with parsley, if desired. Serve warm.