Peel and slice the carrots and parsnips. Slice the celery, dice the onion, and halve, rinse, and slice the leek so no grit remains between its layers.

Heat the olive oil in a large Dutch oven over medium heat. Add the carrots, parsnips, celery, onion, and leek. Cook for about 6 minutes, stirring occasionally, until the aromatics begin to soften.

Stir in the garlic, salt, and black pepper. Cook for 1 minute, stirring constantly, until the garlic smells fragrant.

Add the chicken breasts, thyme, tarragon, bay leaf, and broth. Bring just to a boil, then reduce the heat to low and cover. Simmer gently for 15 to 18 minutes, or until the thickest part of the chicken reaches 165°F.

Transfer the chicken to a clean cutting board and rest it for 3 minutes. Shred it into bite-sized pieces with two forks. Remove the thyme stems, tarragon stems, and bay leaf from the soup.

Return the shredded chicken to the pot and simmer for 2 minutes. Stir in the parsley. Taste and adjust with additional salt, black pepper, and optional lemon juice.

Ladle the hot soup into bowls and garnish with extra parsley, fresh thyme leaves, or cracked black pepper.