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 powder, baking soda, salt, and poppy seeds. Set aside.
03 - In a large bowl, combine the sugar and lemon zest. Use your fingers to rub the zest into the sugar until fragrant.
04 - Add the softened butter to the lemon sugar and beat with an electric mixer until light and creamy, about 2 minutes.
05 - Beat in the egg, lemon juice, and vanilla extract until well combined.
06 - Gradually add the dry ingredients to the wet mixture, mixing just until incorporated.
07 - Scoop tablespoon-sized portions of dough and roll into balls. Place them 2 inches apart on the prepared baking sheets.
08 - Gently flatten each ball with your palm or the bottom of a glass.
09 - Bake for 11–13 minutes, until the edges are set and lightly golden.
10 - Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.