Active Time

　　1 hr

　　Total Time

　　5 hr

　　We recommend using the freshest watercress possible — if not at its best, it can give the sauce a slightly bitter taste. (Try hydroponic watercress; it's generally better than conventionally grown supermarket cress.)

　　Tanis suggests skimming all the fat from the cooking liquid and serving the broth as a first-course soup, garnished with toasted slices of French bread.

　　

Ingredients

Makes 4 to 6 servings

　　

For chicken and vegetables

1 (4-lb) chicken (preferably organic)

　　1 teaspoon salt

　　1/2 teaspoon black pepper

　　1 bunch fresh thyme

　　2 qt chicken stock or canned broth

　　1 qt water

　　1 large onion stuck with 1 whole clove

　　1 head garlic, left unpeeled and halved horizontally

　　1 celery rib

　　1 Turkish or 1/2 California bay leaf

　　8 small leeks (1 1/2 lb; white and pale green parts only), root ends trimmed but leeks left intact

　　12 small (1 1/2- to 2-inch) boiling potatoes (1 1/4 lb)

　　12 small carrots (1 1/4 lb), peeled

　　8 small parsnips (1 1/4 lb), peeled

　　1 large celery root (1 3/4 lb), peeled with a paring knife and cut into 1/2-inch wedges

　　

For green sauce

1 garlic clove

　　2 teaspoons capers, rinsed

　　1/2 teaspoon salt

　　2 cups chopped fresh flat-leaf parsley

　　2 cups coarsely chopped tender watercress sprigs

　　3/4 cup extra-virgin olive oil

　　Garnish: watercress sprigs

　　

Special Equipment

an instant-read thermometer

　　

Poach chicken:

Step 1

Pat chicken dry and sprinkle inside and out with salt and pepper. Stuff cavity with thyme and chill chicken, loosely covered, at least 3 hours (to allow seasoning to permeate meat).

　　

Step 2

Transfer chicken to a 7- to 8-quart heavy pot, then add stock, water, onion, garlic, celery rib, and bay leaf and bring to a boil. Reduce heat and gently simmer chicken, covered, until juices run clear when a thigh is pierced with a skewer and thermometer inserted into thickest part of a thigh (do not touch bone) registers 170°F, about 45 minutes. Transfer chicken to a large platter and let stand, loosely covered with foil, 20 minutes. Reserve cooking liquid in pot, uncovered, and discard onion, celery, garlic, and bay leaf.

　　

Prepare leeks and potatoes while chicken cooks:

Step 3

Starting about 1/2 inch from root end, make a lengthwise cut through middle of each leek (keep leek intact). Wash leeks well under cold running water and drain. Halve potatoes.

　　

Cook vegetables while chicken stands:

Step 4

Bring chicken cooking liquid to a boil, then add leeks, potatoes, carrots, parsnips, and celery root and simmer, partially covered, until tender, about 20 minutes. Carefully transfer vegetables with a slotted spoon to platter with chicken and keep warm, loosely covered with foil. (Reserve cooking liquid for another use if desired cool, uncovered, then chill, covered.)

　　

Make sauce while vegetables cook:

Step 5

Mash garlic and capers to a paste with salt using a mortar and pestle (or mince and mash with a large heavy knife). Transfer to a food processor and pulse with parsley and watercress until herbs are finely chopped. With motor running, add oil in a slow stream and process until smooth. Season sauce with salt and pepper.

　　

Step 6

Serve chicken and vegetables with sauce.

　　Cooks' notes:

　　• Stuffed and seasoned uncooked chicken can be chilled, loosely covered, up to 1 day.

　　• Watercress sauce can be made 2 hours ahead and chilled, covered.