To make the French toast croissants, cut the croissants open. Whisk eggs, cinnamon and milk in a deep dish and dip the croissant halves into the milk and egg mixture. Wait a few seconds for the croissant to soak up some of the liquid.
Heat butter in a frying pan and fry the croissant halves in it until golden brown on both sides, then transfer to a plate. Spread the finished French toast croissants with a little Nutella and serve as hot as possible.
You can also garnish the French toast croissants with some fruit, for example blueberries, before serving.