This recipe makes a ton of ham, so invite some friends over and prepare for leftovers. If you have a smaller ham, adjust the cooking time to a total of 10-15 minutes per pound, with the final 30 minutes at a higher heat.
Heat oven to 325*F. Use a small chef's knife to cut a diamond pattern over the surface of the ham (cut should be about 1/3 inch deep and spaced about an inch apart). Place the ham in a roasting pan and cover with foil. Bake 2 hours.
In a small saucepan, combine the apricot preserves, mustard, and vinegar. Bring to a simmer over medium heat, allowing the preserves to loosen up into thin glaze.
Raise oven temperature to 400*F. Unwrap ham and discard foil. Brush all over with glaze. Return to oven and bake 30 minutes or until the skin is crisped and golden brown.
Remove ham from oven and let sit at least 10 minutes before carving.