Garlic roast lamb with hotpot potatoes

INGREDIENTS

• 1.8kg part-boned leg of lamb
• 5 garlic cloves , sliced
• a few rosemary sprigs
• a few thyme sprigs, plus a few extra to serve
• 50g butter
• 2 large onions , thinly sliced
• 400g pack diced mutton or lamb shoulder, finely choppped
• 2kg large potatoes , such as King Edwards, thinly sliced
• 300g carrots , sliced at an angle
• 3 tbsp plain flour
• 700ml lamb or beef stock , plus 450ml (optional)
• 2 tbsp Worcestershire sauce
• steamed green beans and wilted spinach with nutmeg (optional), to serve