Take 4 lbs raw fish such as 2 lbs each of white salmon and sturgeon or 2 lbs each of beluga and salmon (semga), ½ small jar each of capers and olives, 10 anchovies, and, if desired, 10 small onions. Stone the olives and finely chop. Also chop the capers and anchovies and mix together all the chopped ingredients. If you are adding onions, they must be chopped as well. Cut the fish into very thin slices, spread out the slices [i.e., cover the surface of a napkin with overlapping slices], sprinkle them first with salt and pepper and then with the chopped capers, olives, and anchovies. If desired, strew chopped onions on top. Roll up carefully into a tube, wrap well in the napkin, tie round with a cord, and boil twice as long as a large fish is usually boiled. Cool the fish in the water without removing it from the napkin. When cool, place the fish, still wrapped in the napkin, under a heavy weight for 3 days. Remove the fish roll carefully from the napkin and, when it is time to eat the fish, slice it like sausages. Serve vinegar, olive oil, and mustard separately.