Pulverize the xylitol in the blender, and process the hazelnut and rolled oats in a food processor.
In a large bowl, add ¾ cup (150g/5.3oz) soft butter (or ghee) and ½ cup (90g/3.2) brown sugar. Beat with the help of a hand or stand mixer until you get a smooth and light-colored cream.
As the cream becomes lighter, gradually add 1 cup (120g/4.2oz) powdered xylitol and continue beating.
When you get a fluffy cream, add 3 eggs, one at a time, and continue beating.
To finish, add ½ tsp vanilla extract. Reserve.
In another bowl, mix 2 ¼ cup (180g/6.3oz) hazelnut flour, ¾ cup (90g/3.2oz) rolled oats flour and ¾ cup (90g/3.2oz) arrowroot starch (or potato starch). Once this is done, add the flour to the cream. As you are adding the flour, run the mixer on low speed or do it by hand with the help of a spatula. (The flour must be added very slowly to don't lose aeration, as the final result could ends in a hard cookie!) When all the flour is combined with the cream, add 1 tsp of baking soda and 1 pinch of salt. Finally, add 1⅓ cup (250g/8.8oz) chocolate chips to the dough and stir it with light movements.
Rest the dough in the fridge for at least 15 minutes.
Once the cookie dough is ready, portion it with the help of an ice cream scoop. (I highly recommend using a scoop. Using a scoop ensures that all the cookies are uniform in size so that they bake evenly.) Place the cookies evenly spaced on baking sheets, and space them around 3 cm apart. The dough will spread when baking.
Take the cookies shaped dough once again to the fridge for another 10-15 minutes.
While the gluten-free cookies rest in the fridge, preheat the oven to 180°C for 10 minutes.
Bake the cookies for a total of 15 minutes or until the edges of the cookies are golden brown!