Take a large casserole or pot and add the Gammon along with the, carrot, onion, celery, cinnamon, Bay Leaves and peppercorns. Top up with the Coca Cola to fully cover the gammon and over high heat bring to a boil. Reduce heat, cover the lid and simmer for 2 ½ hours making sure that the gammon is submersed. If necessary, top up with more Coca Cola.
Remove the Gammon from the pot and set on the kitchen bench to cool. In the meantime, preheat the oven to 190 degrees C, air circulation.
When the gammon has cooled, carefully cut and remove the net. Then score the fat side diagonally in 2 cm lines and then crossed to become diagonally scored.
Prepare the glaze by mixing the syrup, mustard vinegar and All-Spice. Place the gammon in an oven proof baking dish lean side down and baste with half the glaze and bake for 15 minutes. Remove from the oven, brush the remaining glaze and bake for 30 more minutes.
Take out of the oven and let rest for at least 20 minutes before carving. Can be made on day ahead and carved cold the day of serving.