Heat the butter in a large pot or dutch oven over medium heat. Add the onions and sauté them for 5-7 minutes or until they start to soften and turn translucent. Add the carrots, celery, garlic, and mushrooms and cook for 3-4 minutes or until the mushrooms reduce in size a bit. Stir the veggies as you add the flour to coat everything evenly, let cook 1 minute.

Stream in the cold milk and 3 cups of chicken broth while you whisk. This will help prevent any lumps. Allow the soup to reach a gentle simmer and start to thicken, about 5-7 minutes. Add the seasoning blend, shredded chicken, peas, and corn and season with a pinch of salt and pepper.

Bring the soup back to a gentle simmer - you do not want it to boil. Cover, and reduce the heat to just above low and let simmer gently for 12-15 minutes.

Remove the lid, stir in the cheese one handful at a time and allow each handful to melt in before adding the next. Season with additional salt and pepper to taste. You can add the cooked egg noodles into the soup at this point or place them in individual bowls. I like to keep them separate from the soup because we always have leftovers! Thin the soup with additional broth to desired consistency. You may need additional broth when reheating leftovers.