• Bring a small saucepan of water up to a boil. Take it off of the heat and immediately add the tarragon stems and all. Let sit for 30 seconds, before transferring to an ice bath.
  28g (1oz) fresh tarragon
• Pat the tarragon dry and transfer it to a food processor or blender. Set the blender to low and stream in the oil. Increase the speed until the herbs are thoroughly blitzed.
  ½ cup olive oil
• Line a fine mesh strainer with cheese cloth and place it over a jar. Pour the herb oil into the cheesecloth and form it into a bundle. Squeeze the bundle to extract the oil. Seal and transfer the oil to the fridge. The tarragon oil will keep for 2-4 weeks.

For the Soup

• Season the chicken liberally all over with salt. *** Set the chicken in a large heavy bottom pot and add the carrots, onion, celery, and thyme.
  1 whole chicken **, 3 carrots, 3 stalks celery, 1 yellow onion, 8 sprigs fresh thyme
• Lop the top off of the head of garlic and add it to the pot as well. Pour cold water into the pot until the chicken is fully immersed. Place the pot over high heat and bring to a boil. Reduce to a simmer and add the salt. Let simmer uncovered for 1 hour.
  1 head garlic, 1 tbsp salt
• After the hour has past, remove the chicken and set it aside to cool. Leave the broth to simmer for another 40 minutes to deepen in flavor. When the chicken is cool enough to handle, shred the meat and set it aside.
• Once 40 minutes has past, taste and season the stock accordingly with salt. Drain the stock and discard the solids.
• Return the pot to the heat and add the butter. Once the butter has melted, whisk in the flour to make a roux. While whisking constantly, slowly ladle in six cups of the chicken stock followed by the milk. Stir in the Dijon mustard and the shredded chicken. Let simmer for 15 minutes.
  ½ cup unsalted butter, ½ cup all-purpose flour, 1 cup milk, 1 tbsp Dijon mustard
• Take the soup off of the heat and stir in the lemon juice. Ladle the soup into bowls and garnish with the tarragon oil and the watercress. Serve immediately.
  Tarragon oil, 1 cup fresh watercress, ½ lemon