How to Make It
Preheat the oven to 325°. Heat the oil in an enameled cast-iron casserole. Season the lamb with salt and pepper; cook over high heat until browned all over, 15 minutes. Transfer to a plate. Add the carrot, onion, garlic, anchovies, capers and tomatoes to the casserole. Cook over moderate heat, stirring, until lightly browned, 8 minutes. Add the Madeira and bring to a boil; add the stock and bring to a boil. Return the lamb to the casserole; season with salt and pepper. Cover and braise in the oven for 1 hour, until tender.
Cook the potatoes in boiling salted water until tender, 20 minutes. Drain and cook the potatoes in the pot to evaporate any water. Add the butter and buttermilk and mash. Season with salt and pepper.
Raise the oven heat to 425°. Set the casserole over high heat and boil until the juices reduce by half, about 15 minutes. Mash the garlic into the juices. Spoon the stew into six 1 1/2-cup ramekins; set on a sturdy baking sheet. Mound the potatoes on top; bake for 25 minutes, until browned in spots. Let rest 20 minutes, then serve.