Place trimmed chicken breasts in the bottom of a 6-quart or larger slow cooker.
Add chopped onion, carrots, celery, garlic, dried thyme, rosemary, salt, pepper, and bay leaf (optional).
Spoon chicken base over the ingredients, then pour in chicken broth.
Stir gently to combine, then cover the slow cooker.
Set the cooker to LOW for 6-8 hours or HIGH for 3-4 hours.
Once the chicken is cooked, remove it from the slow cooker and place it in a mixing bowl.
Shred the chicken with a fork, then discard the bay leaf (if used).
Return the shredded chicken to the slow cooker.
Cook the egg noodles al dente according to package instructions.
Add the cooked noodles to the soup, cooking on LOW for an additional 5 minutes.
Serve with minced parsley and black pepper.