Greek Lamb Moussaka

Name: Greek Lamb Moussaka
Ingredients: 400g (14oz) potatoes, scrubbed; 1 medium onion, peeled and finely chopped; 2 garlic cloves, peeled and crushed; 350g (12oz) lean lamb mince; 175g chestnut mushrooms, sliced; 1 x 400g tin chopped tomatoes; 150 ml vegetable or meat stock; 1 good slurp of Worcester sauce; 2 tbsp chopped fresh parsley; 1 tbsp chopped fresh rosemary; 1 medium aubergine, sliced; 1 medium egg; 100g low – fat soft cheese; 150g 0% fat Greek yogurt; Freshly ground black pepper