Make dough first. In the bowl of a food processor, place the flour and salt. As machine runs, drop in the butter and pulse to create a grainy mixture. Add sour cream or yogurt and process only until a ball forms. Remove from machine and pat on a lightly floured board into a disc. Chill while preparing filling. Prepare onions by sauteeing in oil until golden. Do this slowly. Remove from heat. Boil potatores. Remove skins and mash well. Stir in beaten eggs, melted margarine, salt and pepper to taste and onions. Set aside. Using half the dough, roll out on a lightl floured board into a rectangle about 10 by 20 inches. Spread o horizontal edge with one-quarter of the potator mixture. Roll away from you, as for a jellyroll into the centre of the dough. Cut the dough in half, separating the rolled part (or jellyroll you have formed). Cut the roll into about 10 - 12 small pieces. Repeat with remaining ingredients to end up with four jellyrolls. Knishes can be frozen at the point and baked off as needed. Preheat oven to 350. On a lightly greased baking sheet, place the knishes on their ends, that is, cut side down and squish the kinish slightly on its end. Brush very lightly with melted margarine. Bake until almost golden, about 25 minutes, brush lightly with egg wash, return to oven and bake until nicely and evenly browned.

Per serving: 66 Calories; 4g Fat (58% calories from fat); 1g Protein; 6g Carbohydrate; 18mg Cholesterol; 37mg Sodium