Warm the milk in a large pan and break 500g of Christmas pudding into it, resembling making a porridge. Dissolve the cornflour in a little cold water then add to the mixture, stirring frequently to thicken.
In a separate bowl, whisk 8 egg whites and 1 tablespoon of caster sugar together until it forms stiff, glossy peaks. Fold the beaten egg whites carefully into the porridge mixture. Grease a souffle dish with 40g butter and the remaining sugar and spoon the mixture into the dish. Alternatively you can place in smaller individual ramekin dishes, allowing lots of room to rise.
Bake for 6 minutes until risen and golden brown. Remove from the oven, dust with icing sugar and serve immediately with brandy butter ice cream.