6 lb. bone-in leg of lamb
1 French bâtard
1 to 2 Tbs. extra-virgin olive oil
1 bulb fennel, fronds removed and coarsely chopped
1 yellow onion, coarsely chopped
1 carrot, coarsely chopped
1 rib celery, coarsely chopped
Kosher salt, to taste
Freshly ground black pepper, to taste
2 bunches Italian parsley, leaves only
1/2 lb. unsalted butter, melted
2 oil-packed anchovies
2 cloves garlic, or to taste
Ask your butcher to “French” the leg of lamb, removing the shank to expose the bone, and remove excessive surface fat. Remember, however, that lamb needs a coating of fat to keep it moist.
Let the meat come to room temperature, about two hours, before roasting it. Meanwhile, remove the crust from the bread. Process pieces in a food processor until you have one cup of crumbs. Heat olive oil in a large cast-iron skillet over medium-high heat. Add crumbs and cook, stirring frequently, until they are golden brown. You may add a little more olive oil if the skillet seems dry. Transfer crumbs to a paper towel. Wipe out the skillet.
Preheat oven to 400°F. Place fennel, onion, carrot, and celery in a roasting pan and mix them to combine.
Season lamb with salt and pepper. Reheat the large cast-iron skillet over medium-high heat. When hot, sear the lamb on all sides, just to start the cooking process. Remove lamb and set on the bed of vegetables in the roasting pan. Place it in the oven.
While the lamb is roasting, make a persillade to coat it. Place parsley in a blender. With the blender on, stream in melted butter, scraping down the sides as necessary. Add anchovies and blend. Transfer mixture to a bowl. Grate in garlic, preferably using a microplane. Fold in 1/2 cup of bread crumbs.
When the temperature of the lamb measures 100°F closest to the bone (after approximately 40 to 45 minutes), remove roasting pan from the oven. Quickly press the persillade onto all exposed surfaces of the lamb and return it to the oven. Roast it for an additional 20 to 30 minutes for medium-rare (130°F) and about 10 minutes more for medium (140°F).
Remove lamb from the oven and place it on a platter or carving board. Cover lightly by making a tent over it with aluminum foil and let rest for 20 minutes before carving. Scatter remaining 1/2-cup bread crumbs over the carved slices of lamb.