Strain the pineapple and fill up the pineapple juice with cold water to 375 ml. Bring to the boil with sugar and cornflour, stirring constantly.
Add the soaked gelatin and bring the mixture to a boil briefly, then stir well and refrigerate.
Cut the pineapple into small pieces, stir in the cooked pineapple pudding and half of the whipped cream (125 ml). Pour into a mold rinsed with cold water and refrigerate for about 3 hours.
Turn out the dessert and decorate with 4 slices of pineapple and the remaining whipped cream.