Peel 30 boiled potatoes, cool, and chop fine. Mix with 2 chopped herring or ⅛ lb dried, boiled, and chopped white mushrooms. Add green and white onions, dilute slightly with fish or mushroom bouillon, and mix. Form into an oblong bun and pour on mustard sauce with pickles, small mushrooms, finely chopped salted cucumbers, and finely chopped onions, which are essential (use 1 glass in all).