Clean and wash chicken and place in a very large pot with onion, celery, carrots, parsley, 1 teaspoon salt, and ½ teaspoon pepper. Cover with water and place the lid on top.
Bring the mixture to a boil, and allow to boil for about 30 minutes. Then, turn the temperature to low and cook for 2 ½ - 3 hours or until the chicken is cooked and tender.
Drain the chicken and vegetables from the pot, save the cooking liquid!
COOK NOODLES:
Add the cooking liquid back to the pot along with 2 cups of store-bought stock. Cook the noodles as per the package instructions. Drain the noodles when done, reserving the cooking liquid.
CUT UP CHICKEN:
While the noodles are cooking, debone the chicken and cut it into small bite-size pieces.
TO FINISH:
Add the drained noodles back to the pot. Stir in condensed soup and milk to the noodles.
Stir in the chicken pieces and cooked vegetables. Add some of the reserved cooking liquid if the mixture is too dry. Season to taste with salt and pepper. Serve.
Notes
To make ahead, cook the chicken and store it in an airtight container in the refrigerator until you're ready to use it. You can do this up to 3 days in advance.
If you're short on time, you can also use a rotisserie chicken, although you will need more chicken stock to cook the noodles to get the flavor you get by using the water the chicken was cooked in.