Place gammon in a large pot with oranges, lemons, bay leaves, cinnamon, star anise, peppercorns, onions, carrots, and celery. Pour in wine and stock, adding water if needed to cover. Bring to a boil, reduce heat, and simmer for 2 hours, skimming occasionally. Remove from liquid and cool slightly. Carefully remove skin, leaving an even layer of fat. Score fat in a diamond pattern and stud intersections with cloves.
Combine all glaze ingredients in a saucepan. Simmer over medium heat for 10 minutes until syrupy. Preheat oven to 200°C. Place gammon in a roasting pan, brush liberally with glaze and roast for 45 minutes, basting every 15 minutes, until golden and caramelized.
Par-boil potatoes for 10 minutes. Drain well and shake in a colander to rough up the edges. Heat fat in a roasting tin until smoking hot. Toss potatoes with semolina, rosemary, salt, and pepper. Add to hot fat and roast for 60 minutes until golden and crispy, turning occasionally.
Halve pears lengthwise and remove cores. Mix blue cheese, mascarpone, and chopped walnuts. Fill pear cavities with the cheese mixture. Drizzle with honey and garnish with thyme. Serve at room temperature alongside gammon.