Preparing the Lamb: I usually buy a boneless leg of lamb and butterfly it myself. To butterfly the lamb, open it up to lay it flat and then make a few cuts into the thickest parts of the meat, stopping each cut at about the thickness that you want the meat to be. Don't cut too deep or all the way through. This will flatten out the meat some more so it will cook more evenly. Then trim away excess fat and you're ready for the herb rub.