Preparation

A day ahead:

• To make the spice rub, combine all the ingredients in a small bowl.

  Rinse the chicken and pat it dry with paper towels. Sprinkle 1 Tbs. of the spice rub inside the body and neck cavities. With your fingers, work a little of the spice rub under the skin. Set aside 1 Tbs. of the spice rub for the sauce, then sprinkle the remaining rub all over the skin and rub it in to spread evenly. Tuck the wings behind the neck. Cover the chicken and refrigerate overnight.

On the day of grilling:

• To make te sauce, whisk together the ketchup, mustard, molasses, red-wine vinegar, reserved spice rub, and Tabasco sauce in a small bowl.
• Set up a charcoal or gas grill to cook with indirect heat. If using charcoal, pour about 1 to 2 inches of natural hardwood charcoal over the bottom grate (about a single layer). Light a chimney starter full of coals and when they’re covered with ash, pour them over the unlit coals in the grill. When the fire has burned down and the coals are glowing embers covered with ash, use long tongs or a grill rake to divide the coals into two equal piles on opposite sides of the grill.
• If using gas, set the outside burners to medium high and leave the center burner off.
• While the grill is heating, open the can of beer and poke several holes on top of the can using a churchkey-style can opener. Pour out (or drink) half of the beer. Using a funnel, fill the can with the sauce. Gently swirl the can to mix. Put the can in the center of a 10- to 12-inch ovenproof skillet. Holding the chicken upright with the opening of the body cavity facing down, lower the chicken onto the beer can. Stabilize the chicken with its legs so that it stands up.
  

Grill the chicken:

• Set the skillet in the center of the grill, or in the area where there’s no direct heat. Put an oven thermometer on the grate next to it. Cover the grill. Adjust the vents or burners to keep the temperature between 350° and 375°F, and grill the chicken until an instant-read thermometer registers 175°F at the thickest part of the thigh, 45 min. to 1-1/4 hours. If the grill temperature is correct, the chicken should start to lightly brown after 15 min. (If using charcoal, check every 15 min. and if the temperature drops below 300°F or if the coals have burned down very far, add a handful of fresh charcoal to each pile of coals.)
  
• Carefully transfer the chicken and beer can to a cutting board. Let it rest for 5 min. Meanwhile, line a platter with the lettuce leaves. Using wads of paper towels to protect your hands, carefully remove the chicken from the beer can (ask for help if the can is stuck). Discard all but 1 Tbs. of fat in the skillet and then pour the contents of the can into the skillet. (If the skillet drippings have burned, pour the contents of the can into a clean saucepan.) Bring to a boil over medium-high heat and cook, whisking, until it has reduced slightly and thickened to a nice gravy consistency, 2 to 3 minutes. Carve the chicken into eight pieces and arrange on the platter. Garnish the chicken with the chopped scallions and citrus zest. Put the sauce in a sauceboat or bowl and serve alongside