Firstly, preheat oven to 190C/Gas Mark 5 and line a large baking tray with baking paper. Cream the butter and sugar together until smooth. Then add the flour until it resembles a smooth paste. Add in the chopped chocolate or chips and mix together until evenly combined.
Roll out onto a lightly floured work surface until roughly 1cm thick. Using a rectangular cutter, cut out biscuits and place onto the prepared baking tray evenly spread out. Sprinkle with a little caster sugar, and then chill in the fridge for 20 minutes.
Then bake in the oven for 15-20 minutes, or until lightly golden brown. Set aside to cool on a wire rack.
Once the biscuits are completely cool, melt the dark chocolate over a bain-marie ensuring the bottom of the bowl does not touch the water. Whilst melting, spread the nibbed hazelnuts evenly onto a plate.
Once the chocolate has fully melted, dip the biscuits in halfway and then lay either side flat onto the nibbed hazelnuts, ensuring they stick to the chocolate. Then place on baking paper to set.