Place the bacon in a large saucepan along with the bay leaf, peppercorns, vinegar and onion and cover with cold water. Put a lid on the saucepan and bring to the boil. Then reduce the heat and gently simmer for about an hour - allow 20 minutes per ½ kg.
When the bacon is cooked take it out of the saucepan and place in a roasting tin lined with parchment paper or tin foil. Heat the oven to Gas Mark 7, 220°C (425°F).
Allow the bacon to cool while you make the glaze. In a small bowl mix together the mustard, orange zest, soy sauce, cider vinegar, ginger and brown sugar. Remove the rind from the joint and score the exposed fat with a sharp knife to form a diamond pattern. Spread the mixture over the joint. Place it in the oven for 20-25 minutes, basting with the glaze a couple of times until the fat is crisp and golden.
Slice and serve with creamy mashed potatoes and leeks that have been cleaned, sliced and sautéed in a little butter.