To prepare vinaigrette, combine first 6 ingredients in a small bowl; stir with a whisk. Set aside.
To prepare salad, steam cauliflower and broccoflower, covered, 8 minutes or until tender. Drain and place in a large bowl. Stir in watercress and next 7 ingredients (watercress through capers). Drizzle vinaigrette over salad, tossing gently to coat. Serve with egg quarters.