Nutella Centers: Line a baking sheet with parchment paper. With just half of the Nutella (about 4 tablespoons), fill piping bag (or you can use 2 small spoons) to create 16 Nutella centers, they should be no larger than half a teaspoon. Leave in the freezer for 1 hour, until frozen.
Ganache: Heat the cream in a heavy-bottomed saucepan until bubbles begin to form around the edge of the pan. Place the finely chopped milk chocolate and the remaining Nutella into a medium-sized mixing bowl. Pour half of the hot cream over the milk chocolate; allow it to sit for 30 seconds. Then, slowly whisk until smooth. Add the remaining hot cream gradually and mix until all of the cream has been incorporated and the ganache is smooth. Leave to cool in the refrigerator for 15 minutes.
Whip the cold ganache until light and fluffy; place back into the refrigerator for at least 30 minutes or until you are ready to make the truffles.
Working quickly, use two spoons to roll the Nutella centers into the whipped ganache. Working in batches may be best in order to prevent any softening of the ganache and centers. For a smoother truffle, you can use powder-free latex gloves to roll them by hand. Place the truffles back onto a parchment-lined baking sheet and leave in the fridge for 15 minutes.
Melt 8 ounces of milk chocolate either over a double boiler or in the microwave. To melt the chocolate in the microwave, chop the remaining 8 ounces of milk chocolate and place ¾ of it in a small microwave-safe bowl in the microwave for 20 seconds. Stir the chocolate and continue to microwave for 20 seconds at a time, stirring in between, until the chocolate is smooth and shiny. Add the remaining ¼ of the chocolate and stir until smooth.
With two small spoons, pick up each truffle and cover it with the melted chocolate then roll in the ground hazelnut wafers or optional garnishes, allow the truffles to sit for a few minutes until set, serve at room temperature.