Preheat oven to 180˚C (fan).
Line two baking trays with baking paper.
Cream butter and sugar, beat in egg and then the white, add gluten free flour blend, baking powder, and salt, and coconut, and mix to combine.
Roll into balls and gently press to flatten a little between the hands.
Dip top side in extra sugar.
Bake in moderately hot oven 18 to 25 minutes, until golden.