01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk gluten-free flour, baking soda, and salt in a medium bowl. Set aside.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2 minutes.
04 - Incorporate egg, lemon zest, lemon juice, and vanilla extract, beating until fully combined.
05 - Gradually add dry ingredients to wet mixture, mixing until just incorporated.
06 - Gently fold chopped walnuts into the dough until evenly distributed.
07 - Sop tablespoon-sized dough balls, roll in extra granulated sugar, and place on prepared baking sheets 2 inches apart.
08 - Press each dough ball lightly with fingers or glass bottom to flatten slightly.
09 - Bake for 10 to 12 minutes until edges are lightly golden.
10 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack to cool completely.