PREPARE OR DEFROST the chili base. Combine water and the juice of 1 lemon in a 2 litre pot. Keep the lemon for rubbing the cut surfaces of the artichokes as you work. Cut the stems off the artichoke. Trim the tops, leaving a base about 4 cm deep and exposing the center choke. Trim all around the sides and bottom to remove the dark green exterior. Place bottoms in the water as they are done. When the 4 artichokes are trimmed, bring the water to a boil, covered, over high heat and cook for 20 minutes, or until bottoms are tender. Remove from heat and remove artichokes from the liquid. When cool enough to handle, scoop out center chokes and discard. If not using artichokes immediately, replace in cooking liquid and keep in refrigerator. Meanwhile, heat the oil in a Dutch oven or deep ovenproof skillet over high heat on the stove. Add the lamb and saute, stirring, 5 minutes. Reduce the heat, add the artichokes and garlic and cook another 5 minutes. Add the chili base, lime juice and stock. Cover and place in oven for 1 hour. Taste for salt. Arrange the chili in a covered dish, or serve individually in bowls and sprinkle with chopped cilantro. Serve warm tortillas instead of bread and pass sour cream on the side.