In a large stockpot, combine cooked chicken, chicken brother, water, bay leaves, dried thyme, salt, pepper, onion, carrots, and celery. Bring to a boil, cover and simmer until the carrots are tender.
Bring back to a boil and add the noodles and peas. Cook for 5 minutes (15 if noodles are still frozen).
In a small bowl, whisk together milk and flour. Stir into the noodles and cook, stirring the entire time, until the mixture has thickened considerably.