Preheat the oven to 350 degrees and line a 9 x 9 pan with parchment paper.
In a large bowl, add the Nutella, cashew butter, eggs, maple syrup, avocado oil and vanilla extract. Whisk until smooth.
Add the cocoa powder, baking powder, kosher salt, almond flour and arrowroot flour. Whisk until well combined and very smooth. Fold in the chocolate chips and chopped hazelnuts (if using).
Pour the batter into the prepared baking dish. Bake for 20 minutes or until a toothpick comes out clean.
Allow brownies to cool for at least 20 minutes before slicing for best results. Enjoy!