Cut 6 circles from the sponge and place in the ring moulds on a tray. Sprinkle the sponge with the rum. Next make the pineapple juice by peeling and coring the pineapples and blending the flesh in a food processor. Put the pineapple pulp into a pot and boil vigorously for 5 minutes to kill the enzymes in the fruit. Strain the juices until you have 450ml. If the juices are not sweet, add some sugar to taste and stir over heat until it dissolves. Then set the juice aside until it cools.
Put the gelatine powder into a small bowl with 3 tablespoons of cold water and leave to soak for 5 minutes. Then whisk the gelatine into the warm pineapple juice and leave the mixture until it starts to set and then pour over the trifle sponge, about half way up the ring mould. Then place in the fridge to set.
To make the custard, put the coconut milk in a pot and bring to the boil. In another bowl whisk the eggs, sugar and corn flour until pale and thick. Pour the coconut milk over the eggs and sugar and whisk together until combined, then pour the mixture back into the pot and cook on a low to medium heat until the mixture thickens and it coats the back of a spoon. Pass the mixture through a sieve and allow to cool, then pour the custard onto the jellies and put in the fridge to set
To serve, place the trifle on the serving dish and remove the mould. Place some whipped cream on top and garnish with coconut shavings and popping candy and a sparkler (If you wish you can also assemble this trifle in a martini glass).