Make Ahead Tip: Brine the chicken (Step 2) for up to 12 hours.
Buttermilk is a thick, tangy cow's-milk dairy product great for baking, salad dressings and marinades. Low-fat and nonfat versions can be used interchangeably in most recipes. Look for it in quart containers in the dairy section of the supermarket. In a pinch, you can make a substitute: mix 1 tablespoon lemon juice or vinegar into 1 cup low-fat or nonfat milk.
Once the grill is heated, oil a folded paper towel, hold it with tongs and rub it over the hot rack right before placing the chicken on the grill.