Pork hock croque-monsieur

Name: Pork hock croque-monsieur
Prep time: 15 min
Cook time: 2 h 30 min
Total time: 2 h 45 min
Cuisine: French
Ingredients: 2 smoked pork hocks (about 800gm each); 2 litres (8 cups) chicken stock; 300 ml dry white wine; 2 each onions, celery stalks and carrots, chopped; 8 thyme sprigs; 2 garlic cloves; 8 thick slices sourdough bread; 150 gm Gruyère, finely grated; 60 gm butter, diced; 60 gm plain flour; 400 ml milk, warmed; 100 gm Dijon mustard; ½ tsp finely grated nutmeg; 2 cups (loosely packed) watercress; 8 cornichons, halved; 3 golden shallots, thinly sliced on a mandolin; Juice of 2 lemons; 2 tbsp olive oil