Tip the chocolate into a medium bowl. Put the cream and butter in a small saucepan and heat gently until the butter has melted and the cream just gently bubbling.
Pour the cream mixture over the chocolate and stir until smooth. Cool, cover and chill overnight.
To shape the truffles, scoop up generous teaspoons of the mixture and drop onto a chilled baking tray lined with greaseproof paper. Lightly roll the truffles between your palms. Chill again for 1 hour.
Spoon the Hazelnut Chocolate Spread into a small bowl and heat in the microwave for a few seconds until soft.
With a fork, pick up one truffle at a time and hold over the bowl of soft Hazelnut Chocolate Spread. Spoon the spread over the truffle until well-coated. Place on the baking tray and drizzle with any remaining spread. Sprinkle with finely chopped hazelnuts.
Chill for a further hour until set.
The truffles will keep in an airtight container, in the fridge, for 2-3 days. Or, pop them in the freezer for up to a month.
