01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the gluten-free flour, baking soda, and sea salt. Set aside.
03 - In a large bowl, beat the softened butter, hazelnut butter, light brown sugar, and granulated sugar together until light and creamy, approximately 2 minutes.
04 - Add the egg and vanilla extract to the butter mixture; beat until thoroughly combined.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing just until incorporated. Do not overmix.
06 - Gently fold in the dark chocolate chunks and chopped toasted hazelnuts until evenly distributed.
07 - Scoop tablespoon-sized portions of dough onto the prepared baking sheets, spacing them about 2 inches apart.
08 - Flatten each dough ball slightly with the back of a spoon to promote a crisper texture during baking.
09 - Bake for 10 to 12 minutes, or until the edges turn golden and the centers are just set.
10 - Allow the cookies to rest on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.