Peel and cut the onions into wedges. Place the ham in a roasting pan and add the peppercorns, onion and bouquet garni.
Add water until it comes halfway up the side of the pan. Cover the ham with foil (making a tent to allow steam to circulate). Bake for 1½ hours or until pink and cooked through, then remove from the oven and cool for 30 minutes, remaining covered.
While it’s still warm, you will need to carefully remove the skin, keeping the fat attached to the ham. With a sharp knife, score the ham by making diagonal cuts across the leg.
To make the jerk seasoning, peel and chop the garlic and shallots, deseed and chop the scotch bonnets and finely chop the chives. Blend all the ingredients with a decent pinch of salt in a food processor until smooth.
Rub the jerk seasoning all over the ham and scored fat, cover in plastic wrap and pop in the fridge overnight, preferably 24 hours.
Preheat the oven to 180°C/350ºF/gas 4.
Combine the glaze ingredients in a bowl. Remove ham from the fridge, scrape off excess seasoning and bake for 1 hour. Remove from oven, brush with glaze, then continue cooking the ham for another 30 to 40 minutes, basting with glaze every 10 minutes until crisp, golden and sticky.