Preheat your oven to 190C bake.
Add butter, honey, brown sugar and mustard to a small pot. Melt over medium heat, then bring to a simmer. Once simmering, remove from heat. Cut the skin off the ham, leaving the layer of fat attached. Place the ham in a medium roasting dish. Score the top of the ham in a diamond cross-hatch pattern about 1cm deep.
Spoon half of the butter glaze over the ham, then sprinkle over the fennel seeds. Arrange the rosemary inside the dish around the ham.
Roast the ham for an initial 20 minutes. After 20 minutes, spoon over the rest of the butter glaze. Roast for a further 20 minutes, then remove from the oven and baste the ham with the drippings from the roasting dish. Roast for a further 40-60 minutes, basting the ham every 20 minutes, until the ham is sticky, glazed and caramelised.