The bone-in lamb shoulder that I was able to purchase is 8.5lbs. How would the cooking time scale? Do I need to double the cooking time?
What's the weight / time on the original? I don't think doubling in size = doubling in time - and really temperature is better to go by than time since the oven, the cut, and other factors will affect your ultimate cook time. Remember to factor in a decent rest period as well if you are planning a dinner!!