Mix the butter and sugar in a bowl until frothy, add the eggs. Also stir in the Nutella, hazelnuts, flour, baking powder and milk.
Pour into a greased cake tin. Bake in the oven preheated to 180 ° C for 50 minutes. After cooling, cover with chocolate and garnish with Smarties. Personally, I also like to add some smarties to the batter.