From Serena, Food & Stories: Feeding Friends Every Hour of the Day (Stewart, Tabori and Chang, 2004). © 2004 by Serena Bass
Ask the butcher to butterfly the leg (removing the bone and opening the leg to make a flat piece of meat) and then back home spend five minutes with a sharp knife trimming up his or her handiwork. You will divide the leg into individual sections, following the muscles. There's a bit of waste, but you end up with pure meat and a judicious amount of fat, which helps baste the roasting meat, plus the end result is so much easier to carve than a whole leg with bones in it.
Put the oil in a small pan over medium heat. When hot add the rosemary, ginger, garlic, 3 teaspoons of the salt, and pepper. Sauté for 1 minute, then remove from the heat. Allow the mixture to cool, then rub the paste into the lamb. Cover loosely and refrigerate for at least 4 and up to 24 hours.
Take the lamb out of the fridge 2 hours before cooking. Position a rack in the upper third of the oven and preheat to 400°F.
Set a large nonstick saucepan over high heat and heat the pan for 2 minutes. Keeping the heat high, sear the lamb on both sides in batches. Scrape any scraps of rosemary and ginger in the saucepan onto the seared meat after each batch.
Arrange the lamb on a sheet pan and put in the oven to roast. Start checking the smaller pieces for doneness after 10 minutes. The largest piece will take about 20 minutes. If you have a meat thermometer, use it now. My thermometer broke about 6 years ago (memo from the school of antique cooking habits) so I use a metal trussing skewer. I stick the skewer into the center of the meat, wait 5 seconds, then touch the skewer to my cheek. If the metal is warm, the meat is done. This trick caused an uproar of consternation in the catering office, prompting a chorus of "How warm?" ...so maybe a meat thermometer is the way to go. Aim for 350°F.
Allow the lamb to rest for 20 minutes. Thinly slice and serve warm or at room temperature.
Adam Rapoport, editor in chief of Bon Appetit magazine and the website www.bonappetit.com, knows his way around a grill. He has edited an entire book on the subject: The Grilling Book: The Definitive Guide from Bon Appetit.