In recent years, salad greens have enjoyed a culinary renaissance fueled by the American fascination with local and artisan foods—and a spate of books on the health benefits of French eating habits. At fine restaurants, the standard house salad, with chunks of cucumber, tomato and a choice of five fatty bottled dressings, has all but disappeared, replaced by tender heirloom greens, mesclun greens, baby greens and even microgreens, freshly picked and dressed with the lightest touch of...