Spatchcock the chickens (see instructions below), then place them in a large, nonreactive bowl. Combine remaining ingredients in a blender and process to a smooth puree. Pour half this sauce over the chickens, coating them well. Refrigerate remaining sauce, bringing it to room temperature before serving time. Cover and let chickens marinate in the refrigerator for 4 to 12 hours (the longer the better). Use indirect grilling method (see box), placing a drip pan in the center. If using gas, cook on medium.

When ready to cook, oil the grill grate. Place the chickens, skin side up, on the hot grate, reserving any marinade in the bowl. Brush chickens with the marinade, then cover the grill and cook for 30 minutes. Uncover and brush chickens with marinade. Cover and continue grilling until juices run clear from thickest part of the thigh or until an instant-read meat thermometer inserted in thigh registers 180 degrees F. For crisp skin, place the chickens skin side down on the grate directly over the fire for the last 5 to 10 minutes. Using spatulas, carefully transfer chickens to a platter; let stand for 5 minutes before carving. Serve with the reserved sauce.

To Spatchcock a Chicken: Remove and discard the fat inside the body cavity. Rinse the bird, inside and out, then drain and blot dry with paper towels. Place the bird, breast side down, on cutting board. Using poultry shears, cut through the flesh and bone along both sides of the backbone. Cut from tail end to head end; completely remove the backbone. Open the bird like a book, gently pulling the halves apart. Using a sharp paring knife, pierce the top of the breastbone crosswise. Run your thumbs along and under the sides of the breastbone and attached cartilage and pop them out. Spread the bird out flat. For a more attractive bird, turn it over and, using a sharp knife, make a slit in the skin between the lower end of the breast bone and the leg, 1 inch long on each side. Stick the end of the drumstick on that side through the slit.