Prepare the truffle mixture by combining Nutella and heavy cream.
Incorporate the finely chopped hazelnuts into the truffle mixture.
Chill the truffle mixture in the refrigerator for at least 1 hour.
Using a small scoop, portion out the truffles and roll them into balls.
Melt the dark chocolate in a microwave or double boiler until smooth.
Dip each truffle into the melted chocolate, then remove and let excess drip off.
Roll the dipped truffles in cocoa powder to finish.
Refrigerate the finished truffles until the chocolate coating is set.
