1 Preheat the oven to 180°C (160° fan) 350°F gas 4. Line 2 large baking trays with non-stick baking paper.
2 Beat the butter with the sugar and brown sugar until light and fluffy in a mixing bowl.
3 Gradually beat in the egg and vanilla.
4 Mix together the flour, hazelnuts, cocoa powder and baking powder and stir in carefully. Fold in the chopped chocolate.
5 Put teaspoonfuls of the mixture on the baking trays, leaving about 5 cm | 2" between them. Bake for 10-12 minutes until lightly golden.
6 Cool on the baking trays for a few minutes, then place on a wire rack to cool completely.