In a small bowl add 2 ounces (75 grams) of milk chocolate and 3 1/4 ounces (100 grams) of dark chocolate, place over a pot of boiling water (make sure the water does not touch the bottom of the bowl with the chocolate). The remaining chocolate place in another bowl.
Place and candy thermometer in the bowl and allow the chocolate to reach 122F (50C), then remove from heat and stir to combine add the melted chocolate to the remaining chocolate, place the candy thermometer in the bowl and continually stirring the chocolate until the temperature reduces to 90F (32C).
Then add the Nutella and stir with a spatula until smooth and completely combined**. Pour into the Gianduiotto chocolate mold, cover with foil and let the chocolates firm up either in the fridge or room temperature (if your house isn't too hot). Pop out of mold and serve. Enjoy.
**At this point I divided the mixture into two and one part I added the ground hazelnuts.