Preheat the oven to 400ºF.
Heat 1 tablespoon of the olive oil in a large sauté pan over medium heat. Add the shallots and leeks, season with salt and pepper, and cook, stirring, for 1 minute. Add the crawfish tails, season with salt and pepper, and cook, stirring, for 1 minute. Add the spinach and garlic and cook, stirring, until the spinach wilts, about 2 minutes. Remove from the heat and pour into a large mixing bowl. Stir in the cheese and season with salt and pepper.
Place the lamb on a clean work surface. With a meat mallet, pound the lamb to about 1 inch thick. Rub with the remaining 2 tablespoons olive oil and the rosemary. Season with salt and pepper. Spread the crawfish-spinach filling evenly over the meat. Fold the bottom end of the meat inward, then fold both ends into the center. Tie crosswise with butcher’s twine, at 3-inch intervals. Press the cracked peppercorns into the surface of the tied lamb. Put the roast in a large shallow roasting pan and cook until an instant-read meat thermometer reads 130º to 140ºF for rare to medium-rare, about 1 1/2 hours; 145º to 150ºF for medium, about 2 1/4 hours; and 160ºF for well done, about 2 1/2 hours. Remove from the oven and let rest for 10 minutes before carving. Serve warm.
Yield: 10 to 12 servings