A croissant with Nutella combines the best of both worlds: the lightness and butteriness of a croissant with the rich, chocolate-hazelnut flavor of Nutella. No chocolate cake does better.
Buy or bake the croissants according to description on the package.
Let everyone spread their own croissant. Thus, each determines their own amount of Nutella.
You can cut open the croissant and spread the Nutella on it. Personally, I find it easier to spread the Nutella at the bottom and eat the croissant upside-down.