Place the ham in a roasting pan fat-side up. Score the fat with a crisscross pattern. Cook the ham for about 1 hour to allow the scored fat to open up.
In the meantime, in a small saucepan over medium heat, stir together the brown sugar, apple jelly, mustard, vinegar, ginger and garlic along with 2 tablespoons water. Bring to a simmer and cook for about 2 minutes until it has a smooth syrupy consistency.
Remove the ham from the oven. Generously brush the ham with half of the glaze. Place back in the oven and bake an additional 1 hour and 30 minutes, basting with the remaining glaze every 20 minutes. If the ham starts to get too brown, cover with foil. Remove from the oven, cover and allow the ham to rest for 30 minutes before slicing and serving.