Preheat oven to 350 degrees. Place ham on a rack over a roasting pan and roast for 10 minutes per pound. When there is approximately 1/2 hour more to cook remove ham from oven and cut off the skin (if it has not already been removed by the butcher) exposing the fat and score the fat in a diamond pattern. In a small saucepan mix together the brown sugar, mustard and allspice and heat until the sugar melts. Spread the sugar mixture over the ham. Place ham back in the oven and roast for the final 30 minutes. Allow to rest for about 10 minutes before carving. Serve with mustard and horseradish.