Preheat oven to 325 degrees F. Insert meat thermometer into center of ham without touching bone. Place ham in baking dish and pour cider over. Roast in oven, basting with cider every 30 minutes for a total cooking time of 2 1/2 hours (about 15-18 minutes per pound), or until thermometer registers 140 degrees.
Meanwhile, in bowl, combine brown sugar, mustard and pecans.
Remove ham from oven during the last 40 minutes and firmly pat the sugar pecan mixture all over the ham. Return to oven and continue roasting until crust is brown and ham is done. Slice and serve with sauce. Some of the topping falls into the sauce, making it the perfect accompaniment to ham.
Makes 20 to 25 servings.