Line a large roasting pan with foil. With a sharp knife, score the fat all over the ham in a diamond pattern. Place the ham, cut side down, in the roasting pan and cover tightly with foil. Bake for 1 hour.
Meanwhile, reduce the balsamic vinegar to 1/2 cup, by gently simmering it in a medium sauce pan set over low heat. This process should be done slowly, taking approximately 25-30 minutes to complete. When the balsamic vinegar has become thick and syrupy and is reduced by half, remove from heat and whisk in the Dijon mustard.
After baking for an hour, remove the ham from the oven and increase the oven temperature to 350.
Using a pastry brush, liberally apply the balsamic glaze all over the ham, paying special attention to working it in to the scored portions. Cover just the shank end with a small piece of foil to prevent it from burning. Return the uncovered ham to the oven and roast for approximately 35 minutes, or until the glaze has caramelized and the ham is golden brown.
This recipe uses Frescolio's Maple Dark Balsamic Vinegar. You could also try it with any of the following balsamic vinegars for a different taste: