Preheat the oven to 175°C and immediately use the heat generated to melt the chocolate on a heatproof plate
Mix the first four ingredients until the sugar is properly dissolved
Mix the ground hazelnuts with the baking powder into the butter
Add the melted chocolate and pour the (quite soft) mixture into a baking pan
Bake at 175°C for one hour. After about 20 minutes, put a piece of aluminum foil over it so that it does not get so dark
