Put the egg noodles in a large pot of salted boiling water. Cook for two minutes less than the package instructions for al dente.
Drain and rinse in cold water and set aside until needed.
Preheat the oven to 350 degrees F.
Place the unsalted butter in a large pot over medium heat.
When the butter is melted, add the all-purpose flour to the pot and stir to combine. Cook for 2-3 minutes to cook the raw flavor out of the flour. This is the roux. Don't let it burn or get dark.
Add the chicken broth, one cup at a time, to the roux, whisking to combine. When all of the broth has been incorporated.
Add the milk and sour cream to the sauce, heat for 2-3 minutes until the sauce is thickened to the consistency of a cream soup.
Remove from the heat, and the salt, black pepper, onion powder, and garlic powder to the sauce. Whisk to combine and set aside until needed.
Add 1½ cups of shredded cheddar cheese, parmesan cheese, chicken, peas and carrots, and egg noodles to the sauce. Stir to combine
Pour the mixture into the buttered casserole dish.
Sprinkle the remaining cheddar cheese on top of the mixture.
Place the dish on the center rack of the preheated oven and bake for 30-40 minutes until golden brown, hot, and bubbly.
Cool for 10 minutes before serving.
Garnish with chopped parsley and serve.