Preheat the oven at 200 degrees Celsius.
Chop the chocolate in small bites.
Pour flour, hazelnuts powder, baking powder and salt in a bowl and mix together with a wooden spoon.
In another bowl mix the egg and the oil with an electrical mixer. Add the milk and mix a little longer.
Pour the egg and oil mixture in the bowl with the flour and mix together with a wooden spoon.
Add the chocolate bites and mix well.
Place muffin forms on a baking sheet and spread evenly the batter in each of the forms.
Place the muffins in the middle of the oven for 15 minutes or until the surface is golden brown.