Step 1Place the potatoes in a steamer basket set over simmering water. Arrange the cabbage wedges in a single layer over the top of the potatoes. Cover them and steam until the potatoes and cabbage are tender, about 25 minutes.
Step 2While the vegetables are steaming, toast the caraway seeds in a small skillet sprayed with nonstick cooking spray over medium heat, stirring, until the seeds turn light brown and are fragrant, 1 to 2 minutes. Remove them from the heat and cool slightly. Stir the seeds, onion, garlic and salt into the yogurt until blended.
Step 3Divide the steamed vegetables among serving dishes and spoon over the caraway yogurt.