01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the gluten-free flour blend, baking soda, sea salt, cocoa powder, and espresso powder until evenly distributed.
03 - In a large bowl, use an electric mixer to beat the softened butter, walnut butter, brown sugar, and granulated sugar on medium speed until creamy and smooth, approximately 2 minutes.
04 - Add the egg and vanilla extract to the butter mixture, beating until fully combined and the mixture appears uniform.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Avoid overmixing.
06 - Using a spatula, gently fold in the chocolate chips and chopped walnuts until evenly distributed throughout the dough.
07 - Scoop tablespoon-sized portions of dough and roll into balls. Place on the prepared baking sheets, spacing approximately 2 inches apart.
08 - Bake for 10 to 12 minutes, until the edges are set but the centers remain soft and slightly underbaked.
09 - Allow cookies to rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely before serving or storing.