Drain the meat next morning but reserve the marinade.
Put the leg on a rack, fat side up.
Brush with marinade and broil for 10 minutes on each side or until golden, baste occasionally.
Place lamb on middle rack lower temp to 325f and roast until just pink apprx 2 hrs (depending on the size of the roast)- Check internal temp and if done ahead of the time remove from oven and cover with foil.
Remember that the lamb will continue to cook even out of the oven.
For the last 40 minutes roast some potatoes around the roast.