Preheat oven to 325°F. Place ham in a roasting dish cut side-down and cover with foil. Bake for 2 hours.
In a small saucepan, combine the butter, honey, rosemary, and garlic. Bring to a boil and whisk until smooth. Simmer for about 5 minutes until thickened.
Increase oven temperature to 400°F. Remove foil from roasting dish and brush ham with glaze. Cook for an additional 30 minutes, glazing ham about every 10 minutes.