In a large pot, combine the whole chicken, green parts of leeks, chopped celery, 1 chopped onion, 2 chopped carrots, thyme, bay leaf, salt, and pepper.

Cover with water and bring to a boil.

Reduce heat and simmer for 1 hour or until the chicken is cooked through and tender.

Remove the chicken from the pot and set aside to cool.

Strain the broth through a sieve and discard the solids.

Return the broth to the pot.

Once the chicken is cool enough to handle, shred the meat and discard the bones and skin.

Set the shredded chicken aside.

In a separate skillet, fry the diced bacon until crispy.

Remove the bacon from the skillet and set aside, leaving the bacon fat in the skillet.

In the skillet with the bacon fat, sauté the chopped leeks, celery, and onions until softened.

Add the sautéed vegetables to the pot with the chicken broth.

Add the diced potatoes and bring to a simmer.

Cook until the potatoes are tender, about 15-20 minutes.

Using a blender or immersion blender, puree the soup until smooth.

Alternatively, pass the soup through a sieve for a silky texture.

Season the soup with salt and pepper to taste.

Serve the soup hot, garnished with the crispy bacon and chopped fresh chervil.