Place the gammon joint in a large pot and add the onion, bay leaves and mustard powder. Top with the ginger ale, mango juice and additional stock to cover the meat. Bring to a boil over high heat.
Once boiling, reduce to a medium heat. Cover and simmer for about 40 minutes per kilo or according to instructions on the packaging.
Once cooked, carefully remove the gammon joint from the pan and place on a baking sheet to cool slightly.
Preheat the oven to 180° C.
Meanwhile, to make the glaze: in a small pan over a medium heat, combine the glaze ingredients and bring to a boil, reduce heat to low and cook until slightly reduced and glossy, for about 8-10 minutes.
Carefully remove the netting or string and the skin from the gammon joint. Using a small paring knife cut the skin away from the fat, leaving a small layer of fat on top of the gammon.
Score the fat in a diamond pattern and cover the gammon with the glaze, making sure to reserve at least half of the glaze.
Roast the gammon joint for 20 – 30 minutes, glazing again halfway through.
To serve, garnish with mango slices, carve and serve slices on a platter.
