Prepare a trout mousse, mold it in egg-molds, and garnish the center with trimmed prawns' tails. Let the mousses set; then turn them out of the molds and lay in a deep entree-dish. Between each place a few prawns, the tails of which should be shelled. Cover the whole, slowly, with some good half-melted jelly, add a few sprigs of chervil, and fill up the dish with jelly, so as to completely cover the mousses.