Preheat oven to 350°F and line two baking sheets with parchment paper.
In a large bowl, cream together the softened butter and 1 cup sugar until light and fluffy, about 3 minutes. Beat in the egg, lemon juice, and lemon zest until well combined.
In a separate bowl, whisk together the gluten-free flour, almond flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Shape dough into 1-inch balls and roll each ball in coarse sugar to coat. Place on prepared baking sheets about 2 inches apart.
Bake for 10-12 minutes until edges are just set but centers still look slightly soft. Cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.