In a large pot combine the stock, entire chicken, 2-4 celery stalks with leaves, onion, chopped carrot, garlic, peppercorns, and thyme sprigs. Bring to a simmer over medium heat. Then, cook on low heat simmering for about 1 1/2 hours. Turn the chicken over once.
When the chicken is cooked through, transfer it to a platter to cool. Remove the meat and place it in a bowl. Discard the bones, giblets and skin.
Strain the broth and discard the chopped vegetables and herbs.
In the meantime mix the chicken pieces with the mustard.
Pour the broth back into the pot and bring to a simmer over medium heat. Add 12 whole baby carrots, the turnips and potatoes. Cook for about 10 minutes.
Add the chicken (mixed with mustard), cabbage, cauliflower, leeks, and the remaining chopped celery (leaves removed) Adjust seasoning with salt and pepper to taste.
Let the pot simmer for about 1/2 hour on low heat until flavors are blended and vegetables are soft.
Scoop the chicken and vegetables into individual soup bowls. Add some broth on top. Sprinkle with fresh chopped thyme.
Serve with fresh Artisan Bread.