Mix milk with sugar and Nutella (possibly in a mixing or shaking beaker) and place in a saucepan. Remove 5 tablespoons of this and stir in the cornstarch until smooth.
Bring the milk to the boil, mix in the mixed cornstarch. Bring to the boil briefly, stirring constantly.
Pour the hot pudding into cold-rinsed pudding molds or cups. Cover with foil, allow to cool and turn out onto a plate.
You can leave out the sugar depending on your taste.