Start by setting your chicken breasts in the bottom of the crock pot. While that's in place, slice up your carrots and celery and dice your onion. Keeping the vegetable pieces a similar size helps everything cook at the same rate.
Scatter the sliced carrots, celery, and onion right on top of the chicken breasts. If you like a little extra flavor going in, add a small pinch of salt and pepper now, though I usually hold off until the end.
Pour the chicken broth over the chicken and vegetables until everything is nicely covered. This liquid is what turns into that comforting broth you'll be spooning up later, so don't skimp on it.
Cover the crock pot and cook on low for 6 to 8 hours. Low and slow is what makes the chicken so tender it practically falls apart on its own, so try to resist the urge to bump it up to high.
About 10 minutes before you're ready to serve, use two forks to gently shred the chicken right in the pot. It should pull apart with almost no effort at all, which is one of my favorite parts of this recipe.
Stir in the uncooked egg noodles and fresh parsley once the chicken is shredded. Cover again and let everything cook until the noodles are just tender but not falling apart.
Give the soup a taste before serving and adjust the salt and pepper if needed. Ladle it into bowls while it's hot and enjoy that first cozy spoonful.