Combine Potatoe, Leeks, Parsley And Stock. Simmer For 20 Minutes. Mash Coarsley In Pot. Saute Sorrel In Oil Until The Sorrel Stops Giving Off Water. Add Sorrel And Oil To The Soup. Simmer For 10 Minutes. Combine Yogurt Or Sour Cream With Eggs, Beat Well. Add To Soup, Stirring Constantly. Serve.