01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together the gluten-free flour, baking powder, and salt in a medium bowl. Set aside.
03 - Beat the softened butter and sugar in a large bowl until light and fluffy, about 2 minutes.
04 - Mix in the egg, lemon zest, lemon juice, and vanilla extract until well combined.
05 - Gradually add the dry ingredients to the wet mixture, mixing until just incorporated.
06 - Stir in the chopped thyme leaves until evenly distributed throughout the dough.
07 - Scoop tablespoon-size portions of dough onto the prepared baking sheets, spacing them about 2 inches apart.
08 - Bake for 11 to 13 minutes, until the edges are lightly golden.
09 - Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.