Skin and clean the eel and cut into 1-inch pieces. (Get your favorite fish market to do this, if you can. These members of the fish clan have a habit, disconcerting to most housewives, of wriggling and leaping long after their heads have been cut off.) Remove all bones and replace with chopped parsley. Tie each piece with thread. Cook in salted water until tender. When done, take each piece from the liquid and let cool. Remove thread. Strain the hot fish liquid and add 2 cups of it to the geltain whick has been soaked in the ¼ cup of cold water. Stir until gelatin is dissolved.
Cover the bottom of a ring mold with about half of the aspic and lot cool. When it has jellied, place small pieces of eel over the entire surface of the aspic. Cover with the rest of the jelly and allow to set.
Whip the cream until stiff. Add the horseradish, salt, sugar and the vinegar. Place a dish of the creamed-horseradish mixture in the center of the serving platter on which the eel salad has been unmolded on lettuce.
As a main course, a 3-pound eel will serve 6 people. It will serve many more as one of a number of smørgåsbord dishes.