4 (16-ounce) or larger wine glasses or snifters (note that the idea of a trifle is to see the layers)
Dissolve gelatin and sugar in boiling water. Add cold water and porter. Cover and set aside at room temperature.
For the creme anglaise:
Pour the milk and heavy cream into a heavy bottomed saucepot and scrape the seeds from the vanilla bean into the pot (or add vanilla extract). (If using a vanilla bean, put the vanilla pod in the pot as well.) Add half the sugar to the pot and bring to a simmer (just below a boil). In a small bowl whisk together the egg yolks and the rest of the sugar and temper it by adding a small amount of the heated milk mixture to the bowl while whisking constantly (known as a liaison). Now pour the liaison (egg mixture) into the milk pot, stirring constantly. You are only heating it. Do not boil. Do not cook. The idea of a liaison is to incorporate the eggs and avoid making them into scrambled eggs! You want the mixture to begin to thicken so it will coat the back of a spoon. Remove from heat and allow to cool, then remove vanilla pod and discard, and refrigerate until chilled.
Spoon fruit cocktail into each glass as a base layer. Follow with a layer of cubed pound cake, then a layer of sliced bananas. Spoon about 1/3 cup gelatin/porter mixture on top of the fruit and refrigerate for 2 to 4 hours until the gelatin is set.
A few minutes before serving, make the ganache, place the chocolate in a small heatproof bowl. Bring the cream to just under a boil in a small saucepan. Pour the cream over the chocolate and let sit for about 1 to 2 minutes. Stir gently with a rubber spatula until the chocolate is melted and smooth. If the chocolate is not melting readily, nest the bowl in another bowl of very hot tap water.
Spoon creme anglaise over the chilled trifle and drizzle with ganache. Spoon whipped cream on top to finish.