1. Preheat the oven to 180°C. Line a square 20 x 20cm baking pan with parchment paper.
2. In a Bain-Marie pot, melt the butter, chocolate chips and chocolate chunks. When melted, add the hazelnut spread and mix until incorporated. Let it cool.
3. In a large bowl, beat the eggs and sugar with an electric mixer on medium speed for about 3 minutes. Beat in the vanilla extract. Stir in the cooled chocolate mixture with a rubber spatula. Add the flour, cocoa powder and salt and fold until well combined.
4. Pour the mixture into the prepared baking pan. Bake for 35- 40 minutes. Do not overbake. (A tester stick should come out with some thick crumbly batter on it). Let cool to room temperature, cut in pieces and enjoy!