Preheat your oven to 180°C.

Place the ham in a baking dish, skin side up, and pour half of the cola over it.

Cover and bake the ham in the preheated oven.

Meanwhile, in a pan, combine the remaining cola, rum, brown sugar, and orange marmalade. Stir well.

Let this mixture simmer on low heat until it reduces by two-thirds (about 40 minutes).

Uncover and remove the ham from the oven.

Glaze the ham with one-third of the reduced cola mixture.

Return the ham to the oven for 1.5 hours, brushing it with more glaze every 15 minutes until it's dark and sticky.

Let the ham rest for 15 minutes before carving.