1) Preheat the oven at 180°C. Line and grease a baking tin/brownie pan with baking paper, set aside.
2) Combine all ingredients in a blender except the nuts and chocolate until smooth or in a large bowl (make sure you fave finely grated the baby marrow if you are not blending it).
3) Once combined and half of the nuts and chocolate, spoon out the mixture into the lined brownie pan and smooth out.
4) Sprinkle over the remaining chocolate and hazelnuts, then bake for 20-30 minutes.
*If you like a gooey brownie, check it after 15 minutes, depending on how deep your baking tray is, if you lightly move the tray or tap the top, the center should be firm but when if you skewer it, the skewer should not come out completely clean, THEN ITS PERFECT!
5) Allow to cool completely before slicing and transferring onto a wire rack.
6) Once completely cooled, store in an airtight container in the fridge (they will keep for a week or a month in the freezer, if you can resist).