Paradoxically, the large, delicately flavored globe artichoke, typical of the campagna romana, is not the best for the recipes here, except when it is used raw. The smaller, more ovoid, often purple-tinged varieties from elsewhere in Italy are preferable. To trim artichokes: Remove the tough outer leaves of the artichoke and cut off the thorny tips from the remaining leaves. Working 1 to 2 inches (2.5 to 5 cm) above the base, turn the artichoke against the blade of a small, curved knife, removing everything tough and inedible. The stem is edible. If using, cut off the tough bottom, then peel away the stringy outer layers, exposing the tender core. Work quickly when trimming artichokes, and rub them with a cut lemon or drop them into water acidulated with lemon juice to prevent darkening.