First, preheat the oven to 190°C (375°F approx.).
Then, beat the butter, sugar, and vanilla together with an electric hand whisk.
Sift in the ground rice and almonds, and the xanthan gum and salt, then mix and knead into a dough.
Divide the dough into 8 biscuits and form into rectangles on a lined baking tray.
Prick each biscuit with a fork, then bake in the oven for 20 minutes.
Remove the shortbread from the oven when golden brown, transfer to a wire rack, and allow to cool & harden completely before eating.