Heat a 6- or 8-quart Dutch oven over medium heat with 2 tbsp olive oil. Add the onion, salt, and pepper and cook until the onion is soft and translucent, 3 minutes.
1 cup diced onion, 1 tbsp salt, 1 ½ tsp black pepper
Add the carrot, celery, fennel, chicken, and thyme. Cover with 2 quarts of water. Bring to a boil and reduce to a simmer. Cook until the chicken registers 165°F.
Remove the chicken from the soup and add the egg noodles. When the chicken is cool enough to handle, remove and discard the skin. Separate the meat from the bones and shred. Add back to the soup to warm through and serve. Depending on the size of the chicken, add some or all of the meat and store the rest in the refrigerator for up to one week.