1
In a food processor, grind the raw hazelnuts until they reach a coarse flour consistency.
2
In the food processor, combine all the ingredients except for the hazelnut flour and chocolate chips. Process until well mixed into a thick paste (I used an immersion blender).
3
Add the hazelnut flour back into the food processor and pulse briefly to combine, or, if you use an immersion blender, mix it into the paste with a spatula.
4
Transfer the mixture to a bowl and stir in most of the chocolate chips, reserving a few for garnish.
5
Pour the batter into the greased baking dish, smoothing the top with a spatula. Sprinkle the reserved chocolate chips over the top, and some sea salt flakes.
6
Bake for about 25 minutes in a preheated oven at 350F / 175C. The top may still be soft but it will firm up as it cools.
7
Allow the brownies to cool completely on a cooling rack. For best results, refrigerate them for about an hour before serving to allow them to fully set.