Mix the Jell-O as per package directions and refrigerate until it’s half set and thick. The assembly is done in layers: Place cake into the bottom of a glass serving bowl (or divide it up among several individual glass serving dishes). Drizzle rum or sherry over cake. Add a layer of custard. Add a layer of fruit cocktail. Add a layer of Jell-O and allow it to set firm. Add a layer of whipped cream. Garnish with fruit of your choice. Yields 1 large trifle or several individual ones.