This is part of my “bagged barbecue” series. In the past I’ve cooked turkeys, pork roasts, shrimp, and even apple pies in a bag. If you like the moistness of beer-butt chicken, you have to try this cooking method.
Preheat the barbecue to 425-450 degrees for direct and indirect heating, putting a water pan under the unheated side of the grill.
Rub the butter over the outside and inside of the chicken, including under the skin where you can. Cross the chicken’s legs and tie them together. Tie the wings to the body. Sprinkle the garlic salt, rosemary, and paprika all over the chicken. Do not stuff the chicken.
Lay a piece of waxed paper on the bottom, but not on the sides, of a large brown paper grocery bag. Place the bag on a baking sheet or in a shallow roasting pan. Place the chicken, breast side up, on the waxed paper inside the bag. Balloon the bag, so the chicken doesn’t touch the sides, and tie the bag at the very top or staple it after folding over the top inch of the bag.
Place the chicken on the tray on the heated part of the grill and cook for 1 hour. Reduce the heat and move the tray to the unheated side of the grill and cook for 45 minutes.
Transfer the bagged chicken to a serving platter and cut the bag open at the table. Carve the chicken and serve.