Line a tray, loaf pan or small square pan with parchment paper or foil. Set aside.
Add chocolate chunks and butter to a medium microwave-safe bowl.
Microwave on high at 20-second intervals, stirring in between. Continue heating and stirring several times until smooth and melted.
When the chocolate-butter mixture is ready, stir in powdered sugar.
Pour in milk and mix until homogeneous.
Pour obtained mixture into the prepared pan and spread evenly.
Sprinkle chopped hazelnuts on top if you want.
Cover the pan with a piece of plastic wrap or foil and refrigerate for 3 hours.
When the fudge is set, slice it into squares and enjoy.