Preheat oven to 180°C conventional oven (400° Fahrenheit/Gas 6). Line a shallow baking tray with baking paper.
Place the hazelnuts on the prepared baking tray and bake for 3 minutes, or until golden. Remove from the oven and while still warm, transfer the hazelnuts to a tea towel. Work quickly to rub the hazelnuts to remove the skins. Set aside to cool slightly, then process in a food processor until finely chopped. Alternatively use a knife to finely chop. Transfer to a small bowl.
Place the wafers into a food processor and process until the mixture resembles fine breadcrumbs. Alternatively crush with a rolling pin. Set aside.
To make the Chocolate and hazelnut tartufi mixture, place the butter and icing sugar (confectioners’ sugar) into a large bowl. Use an electric mixer to beat the butter and icing sugar together on medium speed until combined. Add the wafer mixture, thickened cream, Nutella and unsweetened cocoa powder (cacao magro). Cover the bowl with plastic wrap and refrigerate for 10 minutes.
Remove the Chocolate and hazelnut tartufi mixture from the fridge. Roll a tablespoonful of the tartufi mixture into a ball (approximately 25g each). Toss in the finely chopped hazelnuts to evenly coat. Place onto a serving plate. Repeat with remaining tartufi mixture. Cover the Tartufi of chocolate and rum (balls) with plastic wrap and refrigerate for 2 hours before serving – buon appetito.