How to Make It
In a small bowl, combine the parsley, garlic, rosemary, thyme and lavender. Spread the lamb on a work surface, boned side up and season generously with salt and pepper. Spread half of the herb mixture over the lamb and roll it into a roast. Tie the lamb with kitchen string at 1-inch intervals. Spread the remaining herb mixture all over the outside of the roast and season with salt and pepper. Let the roast stand at room temperature for 1 hour.
Meanwhile, in a large skillet, boil the stock over moderately high heat until reduced to 1 cup, about 30 minutes.
Preheat the oven to 450°. Set the lamb in a roasting pan and roast in the oven for 10 minutes. Reduce the oven temperature to 350°. Cook the lamb for 45 minutes longer, or until an instant-read thermometer inserted in the thickest part registers 125° for medium-rare or 140° for medium.
Transfer the lamb to a carving board, cover loosely with foil and let stand for 10 minutes. Add the fennel seeds to the roasting pan and cook over moderate heat until fragrant, about 1 minute. Increase the heat to high, add the reduced stock and cook, scraping up any browned bits on the bottom of the pan; season with salt and pepper.
Discard the string. Carve the lamb into thick slices and arrange on a platter. Pour any carving juices into the sauce, spoon it over the lamb and serve.