how long to cook roast leg of lamb
1 Rub 3 tablespoons olive oil over the surface of the leg of lamb. 2  Place on rack in center of roasting pan and place in preheated oven. 3  Cook for 15 minutes at 450Â°F and then lower heat to 350Â°F for rest of cooking time of 1 1/4 hours (or, alternatively, lower heat immediately and cook at 325Â°F for adjusted cooking time). Rub 3 tablespoons olive oil over the surface of the leg of lamb. 2  Place on rack in center of roasting pan and place in preheated oven. 3  Cook for 15 minutes at 450Â°F and then lower heat to 350Â°F for rest of cooking time of 1 1/4 hours (or, alternatively, lower heat immediately and cook at 325Â°F for adjusted cooking time).