Stem ginger & mustard glazed ham

Name: Stem ginger & mustard glazed ham
Prep time: 20 min
Cook time: 4 h
Total time: 4 h 20 min
Cuisine: European, British
Ingredients: 5kg boneless gammon joint (smoked or unsmoked depending on your preference); 2l ginger beer; 1 onion quartered; 2 clementines or satsumas, halved horizontally, plus a few to decorate the plate, if you like; 20 cloves; 3 bay leaves plus a few to decorate the plate, if you like; 2 tbsp English mustard; 4 tbsp ginger syrup plus 3-4 balls stem ginger from the same jar, thinly sliced