Skin chicken. In a 4-1/2-quart Dutch oven place chicken, water, celery leaves, parsley, bay leaf, thyme, salt, and pepper. Heat to boiling. Reduce heat. Cover and simmer for 30 minutes.
Add the onion, carrots, and sliced celery. Cover and simmer about 30 minutes more or until chicken is tender and no longer pink. Remove from heat. Remove chicken; cool slightly. Discard the bay leaf. Remove meat from bones; discard bones. Chop chicken and set aside.
Heat vegetable mixture to boiling. Add noodles; cook for 5 minutes. Stir in peas and 1-1/2 cups of the milk.
In a screw-top jar combine remaining milk and flour. Cover and shake until smooth. Stir into noodle mixture. Cook and stir until thickened and bubbly. Stir in chicken. Cook for 1 to 2 minutes more or until heated through. Makes 6 servings.