Place the gammon joint in a large pot or Dutch oven and cover it with water. Bring the water to a boil and let it simmer for about 5 minutes. Drain the water and rinse the gammon under cold water to remove any impurities.
Return the gammon joint to the pot and add the cola, onion quarters, crushed garlic, bay leaves, and black peppercorns.
Add enough water to the pot to cover the gammon joint. Bring the liquid to a boil, then reduce the heat to a gentle simmer.
Cover the pot with a lid and let the gammon cook for approximately 1.5 to 2 hours, or until it reaches an internal temperature of 70°C (160°F) when tested with a meat thermometer. This ensures that the gammon is cooked through.
Once cooked, carefully remove the gammon joint from the pot and place it on a cutting board. Allow it to rest for a few minutes before slicing.
If desired, you can transfer the gammon to a roasting pan and place it under the grill for a few minutes to achieve a caramelized glaze.
Slice the gammon and serve it hot alongside your favorite sides such as roasted potatoes, steamed vegetables, or a fresh salad.