Place ham in a roasting pan, preferably with a rack. Roast uncovered to an internal temperature of 140 degrees F as measured with an instant-read thermometer. Remove from oven and increase oven temperature to 425 degrees F. Remove the rind except for the part around the bone end and slash slits in the fat. Combine mustard, honey, and brown sugar, and brush over the surface. Return the ham to the oven and bake to an internal temperature of 160 degrees F, about 30 minutes.