Place the thighs in a zip-lock plastic bag, gallon size, with the mustard, hoisin sauce and tamarind. Zip the bag and massage to evenly to mix the marinade and coat the chicken. Marinate in the refrigerator for several hours or overnight.
Preheat the oven to 350 degrees.
Remove the chicken from the bag and place it in a baking dish with the marinade and bake for an hour, basting and turning the chicken several times.
Remove the chicken from the baking dish, and skim off the fat from the sauce. (Lightly blotting the fat layer with a paper towel will draw off most of the fat.)
Return the chicken to the baking dish with skin side up and baste with the sauce.
Place the chicken under a hot broiler for several minutes or until the skin crisps and turns mahogany in color. Serve warm.
The leftover chicken is delicious sliced thin and served over salad greens.
Note: Hoisin sauce and tamarind concentrate can be found in the Asian sections of most grocery stores.
