How to Make It
Using a chef's knife, chop the garlic with the flat-leaf parsley and fennel seeds to form a coarse paste. In a large enameled, cast-iron casserole, heat the olive oil. Add the garlic paste and cook over moderate heat until fragrant, about 1 minute. Raise the heat to moderately high and add half of the lamb pieces. Cook, turning, until lightly browned all over. Transfer the lamb to a bowl and season with salt and pepper. Repeat the process with the remaining lamb.
Add 1/2 cup of the milk to the casserole and cook over high heat for 2 minutes, stirring to scrape up any browned bits. Add the remaining 3 1/2 cups of milk, the heavy cream, rosemary and the seared lamb and its juices. Bring to a simmer, then reduce the heat to low. Cover and cook, stirring occasionally, until the lamb is tender, about 1 hour and 15 minutes.
Using a slotted spoon, transfer the lamb to a bowl; discard the rosemary. Boil the milk mixture over high heat until reduced to 4 cups, about 10 minutes. Working in batches, puree the hot milk mixture in a blender. Return the sauce to the casserole, add the lamb and simmer over low heat until warmed through. Season with salt and pepper and serve.