Cook potatoes and beets in separate medium pots of boiling salted water until tender, about 30 minutes for potatoes and 35 minutes for beets. Drain; cool slightly. Peel vegetables and thinly slice into rounds. Whisk vinegar, oil and coriander in medium bowl. Season generously with salt and pepper. Add vegetables; toss gently to coat. (Can be made 2 hours ahead. Let stand at room temperature.)
