Whisk flour, baking soda, and salt in a bowl. In another bowl, mix melted butter and sugar, then add egg, lemon juice, lemon zest, and vanilla. Combine wet and dry ingredients until just mixed. Chill dough for 3–4 hours or overnight.
Preheat oven to 350°F (180°C). Scoop dough into small balls, roll first in granulated sugar, then generously coat in powdered sugar.
Place cookies on a lined baking tray and bake for 9–13 minutes until cracks appear and centers look slightly soft.
Let cookies cool on the tray for a few minutes, then transfer to a wire rack to cool completely.