Roast the whole hazelnuts on a cookie sheet for approximately 5-8 minutes in a preheated 350F (180C) oven, remove them from the cookie sheet and place in a bowl to cool. Do not let them cool on the cookie sheet or they will bake even more (not a good idea, they could burn).
In a medium bowl over a medium pot of water (bain-marie) add the milk chocolate and butter, melt together and mix until smooth. Let cool, then mix in the Nutella and ground nuts. Cover the bowl with plastic and refrigerate for approximately 15 minutes.
Remove the mixture from the fridge and form into 14 balls, place them on a parchment paper lined cookie sheet or freezer safe plate, slightly flatten the top of each chocolate ball and place one whole hazelnut on each. Place the chocolates in the freezer for 30 minutes.
CHOCOLATE FOR DIPPING
While the chocolates are in the freezer start to make the dipping chocolate, place 3/4 of the chocolate in a bowl on top of a small pot of water (make sure the water does not touch the bottom of the bowl, bring the water in the pot to a simmer. Using a spatula continuously stir the chocolate until it is melted and smooth. Then place a thermometer in the chocolate and bring it to –118F (48C) for Dark Chocolate or 112F (45C) for Milk Chocolate.
Remove the bowl of chocolate from the pot and carefully wipe the steam from bottom of the bowl. Do not let even one drop of water fall into the chocolate because it will cause the chocolate to seize and then your chocolate is completely ruined! So please be careful! Add the remaining chocolate to the melted chocolate, this will help bring down the temperature of the chocolate. Keep stirring until the temperature of the chocolate reaches –89-90F (32C) for Dark Chocolate 86-88F (30C) for Milk Chocolate.
Remove the chocolates from the freezer and dip in the cooled chocolate, place the dipped chocolates back on the plate, let the chocolate harden, can be placed in the fridge to harden, serve. Enjoy!