Make the brine
Combine all the ingredients in a large saucepan and bring to a boil over high heat. Transfer to a bowl or other container and allow to cool, then refrigerate overnight before using.
Make the herb brush
Tie the herb sprigs around the handle of a wooden spoon, or a long-handled carving fork with kitchen twine.
Make the chicken
Put the chicken legs in a large heavy-duty plastic bag or a large bowl and add the brine. Seal the bag or cover the bowl and refrigerate for 3 hours.
Drain the chicken (discard the brine) and pat lightly dry with paper towels. Allow to come to room temperature, approximately 30 minutes.
Prepare a “mature and level” coal bed: lightly tamp the hot coals down to a uniform height of 4 to 6 inches. A cast-iron skillet or a roasting pan will serve you well for this task. If you like, place a clean thin grate or rack directly on the coals; the fire should be very hot. Just before placing the meat on the coals (or grate), use a hair dryer or a piece of cardboard to fan the coals sufficiently to clear away bits of ash.
Season the chicken legs all over with the seasoning blend, then lightly moisten your hands with water and work the seasonings into the chicken. Allow to stand for 5 minutes to develop a “meat paste.”
Moisten the chicken legs on all sides with the butter baste, using the herb brush. Put the chicken legs skin side down on the grill grate or directly on the coals and cook, without moving them, for 2 minutes. Turn them, baste lightly, and cook for 2 minutes, then repeat two more times, basting the chicken each time it is flipped.
Transfer the chicken legs to a platter, skin side up, and baste generously. Allow to rest for 5 minutes.
Remove the grill grate, if you used it. Baste the chicken legs and put 2 legs side by side on each plank. Put the planks on the coal bed with some coals on the exposed corners of the planks and then cover with a grill lid, a large metal bowl, or a domed lid. Cook and smoke for 10 to 12 minutes, or until the juices run clear when a chicken thigh is pierced with a fork.
Make the board dressing and finish the chicken
Mix the olive oil, parsley, and salt and pepper to taste directly on the board. Finely chop the tip of the herb brush and mix
the herbs into the dressing.
Transfer the chicken legs to the cutting board, turning them in the
dressing to coat, then turn skin side up. Sprinkle with the tarragon and
allow to rest for 3 minutes.
To serve, arrange the chicken on plates and finish with a sprinkling of the salt.
Photo: Simon Wheeler