How to cook the Best Slow Cooked Leg of Lamb! Slow roasted at a low temperature, in the oven for 5 hours, so tender it falls off the bone. Real Ale Chutney added as a marinade for the last 45 minutes of cooking for a tasty sticky glaze. What's more, you can use the stock, vegetables and juices leftover from the lamb, to make your own delicious gravy. Perfect Sunday Roast or Holiday dinner to enjoy with the family.