Beat the yolks with a whisk, adding 100 g sugar, until a pale frothy mixture is obtained, then gradually add the cold milk, rum and crumbled biscuits. Separately, beat the egg whites until stiff. Add the egg whites in the cream, folding them in delicately from below to ensure that the mixture does not collapse. Place the remaining sugar in a small saucepan, add ½ tablespoon water and allow the sugar to caramelise into a nut brown colour. Distribute the caramel sauce uniformly over a pudding mould. Pour in the mixture and cook in a bain-marie in a pre-heated oven at 175º for 40/50 minutes, until mixture has solidified. Remove the mould from the oven, leave it to cool and place it in the fridge for a few hours. Turn the mould out onto a serving plate and decorate with whole or crumbled amaretti biscuits.