Preheat oven to 350F.
Begin by cooking the egg noodles for about 2 minutes less than package directions. They will continue to cook in the oven. Drain and set aside.
Melt 2 tablespoons butter in a large skillet. Saute’ onions, celery and carrots until tender. About 7-10 minutes.
Season vegetables with salt, black pepper, garlic powder and thyme.
Sprinkle six tablespoons flour over the cooked vegetables, stir to combine and cook for an additional 2-3 minutes.
Slowly whisk in 3 cups chicken broth and 1 cup milk.
Simmer over medium heat until the mixture is bubbly and slightly thickened.
Remove from heat and stir in sour cream and half of the shredded cheddar cheese (about 1 and 1/2 cups) and stir until well combined.
Combine cooked chopped turkey (or chicken), cooked noodles, and vegetable/sauce.
Pour into a lightly greased 9 x 13 inch casserole pan.
Sprinkle with remaining 1 and 1/2 cups shredded cheddar cheese.
Bake for 30 minutes until cheese is bubbly.