My Albanian grandmother would cook a leg of lamb the morning before we arrived for family get togethers and she always served it at room temperature...In my opinion it can't be beat. Oh and if you want to be naughty...use the lamb fat to roast potatoes and carrots.

I agree with Merrill. You might also let the lamb sit out at room temp for 30 to 40 minutes before reheating.

If possible, I'd cook it the same day you're planning to eat it; if not, I'd cover it loosely with foil and reheat very gently at about 300 degrees F.