Preheat the oven to 180 ° C.
In a bowl, mix the melted butter, sugar, vanilla sugar and salt.
Then add the egg.
Then add the flour and the flour. mix again.
Leave the mix aside and crush the chocolate.
Then add the chocolate to the dough and mix well.
Cut the dough into two equal parts.
Spread the dough thickly on a sheet of baking paper.
Pour Nutella over the dough.
Cover everything with the rest of the dough. (check the video bellow to understand more)
Place everything on a baking sheet and bake for 10 to 15 minutes.