I don’t mind a bit of mint in a marinade for lamb (heavier pieces like bone-in leg), but I normally don’t like mint flavor in the sauce itself. I think this is a legacy of having had one too many poorly prepared lamb roasts with the host using mint jelly to try to cover over the faults of the roast.
Given you have a week, why not get some bone-in piece like shoulder chop or steak, and sacrifice it to make enough lamb stock to proceed with your original plan?
Sounds like a wonderful dinner, by the way. You have some lucky friends!
