Roast spiced leg of lamb

Name: Roast spiced leg of lamb
Ingredients: 1.6-1.8kg (31⁄2-4lb) leg of lamb; 2 tbsp. cumin seeds; 2 tbsp. coriander seeds; 50 g (2oz) blanched or flaked almonds; 1 medium onion, chopped; 6 garlic cloves, roughly chopped; 2 1/2 cm (1in) piece root ginger, grated; 4 hot green chillies, deseeded and roughly chopped; 500 g carton natural yogurt; 1⁄2 level tsp cayenne pepper; 31⁄2 level tsp salt; 1⁄2 level tsp garam masala; 4 tbsp. vegetable oil; 1⁄2 tsp whole cloves; 16 cardamom pods; 1 cinnamon stick; 10 black peppercorns; Flat-leafed parsley sprigs to garnish (optional)