1. Boil the potatoes and celery roots in plenty of water until soft (about 1/2 hour).
2. Saute onion and cabbage in a bit of cooking spray for a few minutes. Add about 1/4 cup water to the pan (I used a wok), cover, and let cook, stirring once in a while, until onion is browned and cabbage is tender.
3. Add scallions after 10 minutes or so. Drain potatoes and celery root, place in a bowl, and mash with a wooden spoon or potato masher (no food processor! it turns potatoes to glue); it should be slightly lumpy.
4. Add the cabbage-onion-scallion mixture and blend well. Season with salt and pepper, to taste.'