Wrap the beets in foil, and roast in the oven at 350ºF for 1.5 hours. Or you can cook them in a slow cooker, also wrapped in foil, on high for 2 hours.
Let the beets cool, peel the skin off, cut the root stems off.
You can either grate the beets or chop them finely.
Add walnuts, prunes, sour cream, kefir, salt and pepper. Mix well.
Allow to sit in the fridge for a couple of hours, or better overnight, for the flavors to develop.