If you love the spicy taste of curry, add the curry paste to the yogurt dip. For a less intense flavor, add the curry powder.
Rinse artichokes under cold running water. Peel off and discard lower petals. Trim stem to one inch or less. Cut off the top 1-inch of artichoke. Trim leaf tips. Immediately rub the cut surfaces with a piece of lemon.
Cook, covered, in a large amount of boiling salted water for 20 to 30 minutes or until a leaf pulls out easily. Invert artichoke to drain.
Meanwhile, in a medium bowl stir together the yogurt, dressing, lemon juice or vinegar, horseradish, onion, and curry paste or powder. If desired, cover and refrigerate for 2 hours or overnight.
Serve artichokes warm or at room temperature. Or, cover and chill thoroughly. To serve, pull off all outer leaves and arrange on a serving platter with dip. Discard sharp inner artichoke leaves and fuzzy choke. Slice artichoke heart (the bottom) and add to platter or reserve for another use.
Garnish dip with green onion, if desired. Makes about 1-1/2 cups dip (twenty-four 1-tablespoon servings).
Up to 24 hours ahead, prepare dip; cover and chill. Trim and cook artichokes. Cover and chill.