In a medium bowl, sift together the caster sugar, plain flour, matcha powder, and baking powder.
In a separate, large bowl, whip the egg whites until stiff peaks form. Stiff peaks means that the egg whites hold their shape when the whisk is lifted.
Gently fold the sifted dry ingredients into the whipped egg whites in three additions. Use a spatula and a light, folding motion to avoid deflating the egg whites.
Gently stir the melted and cooled butter into the batter until it is fully incorporated.
Cover the bowl with cling film and refrigerate the dough for 40-60 minutes.
Prepare Sugar Coating: In a small bowl, combine the caster sugar and icing sugar.
Divide the chilled cookie dough into five equal portions. Roll each portion into a smooth ball. Dredge each ball in the sugar coating, covering it
on all sides.
Place the coated dough balls on the prepared baking sheet, leaving some space between them to allow for spreading.
Bake for 12-15 minutes.
Allow the cookies to cool on the baking sheet before transferring them to a wire rack.
