Heat oven to 325 degrees F. Line a shallow roasting pan with foil.
Remove all packaging materials and place ham on its side, fat side up, on a rack in the prepared pan; cover loosely with aluminum foil.
Heat approximately 15 to 20 minutes per pound until heated through. For instance, I roasted a 10-lb. ham for 2 ½ hours.
While the ham is in the oven, prepare the glaze: In a small bowl, whisk together brown sugar, molasses, vinegar, and yellow mustard.
Once heated through, remove ham from oven. Increase oven temperature to 400 degrees F. Uncover ham, brush or spoon glaze over surface. Return to oven, uncovered, and heat for 10 more minutes.
Remove ham from oven and let stand, covered, for 10-15 minutes before slicing and serving.