Add the sugar and lemon zest to a large bowl, and rub the zest into the sugar.

Add the melted butter and vanilla, and whisk until combined.

Add the eggs and whisk well.

Add the lemon juice and whisk until smooth.

In a separate bowl, whisk together the gluten free flour blend, xanthan gum, baking powder and salt, and add them to the wet ingredients.

Mix with a wooden spoon or rubber spatula until you get a smooth, batter-like cookie dough.

Chill the cookie dough in the fridge for at least 2 hours.

Preheat the oven to 350ºF (180ºC) and line 2 large baking sheets with parchment paper.

Shape about 1 tablespoon (about 17g) portions of the chilled cookie dough into balls, yielding 30-32 cookies.

Roll each ball in granulated sugar and then in powdered/icing sugar until coated.

Place the cookie dough balls on the lined baking sheets, at least 1 ½-2 inches (4-5cm) apart.

Bake one baking sheet at a time for 8-10 minutes or until the cookies have risen and formed cracks.

Allow the cookies to cool on the baking sheet for at least 10 minutes before transferring them to a wire rack to cool completely.