Preheat oven to 325F. Place ham in a shallow roasting pan. Score ham by making diagonal cuts, 1/4-inch deep, in a diamond pattern. Insert an oven-going meat thermometer into center of ham; the thermometer should not touch the bone, if present. Roast for 1-3/4 hours if using bone-in ham or 1 hour if using boneless ham.
Meanwhile, in a bowl combine 3 tablespoons of the brown sugar, the 3 tablespoons mustard, and rosemary. Brush mixture over ham. Roast for 15 minutes more. Meanwhile, for glaze, in a 2-quart saucepan combine the remaining brown sugar, the pineapple juice, and 1/4 cup mustard. Bring to boiling over medium heat, stirring frequently. Remove 1/2 cup glaze to brush over ham. Set aside.
Bake ham 30 minutes more or until thermometer registers 140 degree F, generously brushing with the 1/2 cup glaze several times during baking.
Meanwhile, add pineapple to remaining glaze in saucepan. Bring to boiling; reduce heat. Simmer, uncovered, for 20 minutes. Transfer ham to serving platter. Slice ham and serve with pineapple sauce. Makes 16 to 24 servings.
Grilled Pineapple Slices
Cut pineapples into 1/2-inch-thick slices. Brush each slice on both sides with a little cooking oil; sprinkle lightly with some snipped fresh rosemary. Heat an indoor grill or grill pan. Grill pineapple slices just until they start to brown, 1 to 2 minutes per side, turning once.