Coarsely chop 125 g chocolate and melt it in a bowl on a hot water bath, then let it cool down until it is almost cold/lue warm. Chop 25 g chocolate finely. Roast the nuts in a pan without fat, then let them cool down.
Whip the butter until light and creamy. Slowly add the liquid chocolate coating, cocoa and maple syrup while stirring. Fold in 3/4 of the nuts. Pour nut-chocolate butter into bowls or glasses and sprinkle with the remaining hazelnuts and chocolate pieces.