How to Make It
Rub the lamb with the cumin and fennel; season with salt and pepper. In a cast-iron skillet, heat the oil until smoking. Add the lamb and cook over high heat, turning once, until browned. Reduce the heat to moderate. Add the thyme, garlic and 4 tablespoons of the butter and cook for 5 minutes, basting the lamb with the butter. Turn the steaks and cook, basting, until an instant-read thermometer inserted in the thickest part registers 130°, 5 minutes; transfer to a carving board and let rest for 10 minutes. Thickly slice against the grain.
Pour off all but 1 tablespoon of the fat. Cook the shallot over moderately high heat until softened. Add the wine and simmer until syrupy. Add the stock and simmer until slightly reduced, 3 minutes. Off the heat, whisk in the remaining 2 tablespoons of butter; season with salt and pepper. Serve with the lamb and french fries.