Preheat oven to 275 degrees. Using a sharp knife, score the fat on the ham in a diamond pattern. Place on a baking sheet, cut side down, and cover tightly with foil. Bake for 1 1/2 hours or until an instant-read thermometer inserted to the thickest part reads 145 degrees.
In a small saucepan combine brown sugar, brandy and mustard. Bring to a boil over medium heat and cook until thick and syrupy, about 3 minutes.
Remove ham from oven and increase oven temperature to 350. Brush ham liberally with glaze, making sure to coat all exposed areas. Return to the oven and bake until glaze is sticky, thick and golden about 35 minutes.