Melt the butter in a large Dutch oven or soup pot over medium heat.
Add the onion, carrots, and celery. Cook for 7 to 8 minutes, stirring occasionally, until the onion is soft and translucent.
Add the minced garlic and cook for about 30 seconds.
Pour in the chicken broth. Add the chicken, thyme, poultry seasoning, bay leaf, salt, and black pepper.
Bring the soup to a gentle boil, then reduce the heat to a steady simmer.
Partially cover and cook for 15 to 20 minutes, or until the chicken reaches an internal temperature of 165°F.
Transfer the chicken to a cutting board and shred it into bite-sized pieces.
Add the egg noodles to the simmering broth and cook according to package directions, usually 6 to 8 minutes.
Return the shredded chicken to the pot during the final 2 minutes of cooking.
Remove and discard the bay leaf. Stir in the parsley and optional lemon juice.
Taste the broth and adjust the salt and pepper as needed.
Serve hot.