01 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
02 - In a medium bowl, whisk together the gluten-free flour blend, baking soda, and salt until evenly distributed. Set aside.
03 - In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar using an electric mixer until the mixture becomes light and creamy, approximately 2-3 minutes.
04 - Add the egg, vanilla extract, and instant espresso powder to the creamed butter mixture. Beat until fully combined and smooth.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Do not overmix.
06 - Gently fold in the chopped toasted hazelnuts and dark chocolate chips until evenly distributed throughout the dough.
07 - Using a tablespoon or small cookie scoop, drop rounded portions of dough onto the prepared baking sheets, spacing them approximately 2 inches apart to allow for spreading.
08 - Bake for 10-12 minutes, or until the edges are golden brown and the centers remain slightly soft. Rotate baking sheets halfway through for even baking.
09 - Allow cookies to rest on the baking sheet for 5 minutes to set, then carefully transfer to a wire rack to cool completely before serving.