In a large mixing bowl whisk together the sweet rice flour, sorghum flour, tapioca flour and salt.
Slice the butter very thinly directly from the fridge and add to the flour. Rub the mixture between fingertips until roughly shorn. It’s okay that the butter is still in largish pieces.
Whisk one egg with the egg white from the second egg in a small bowl. Save the extra egg yolk for later for sealing the pastry.
Make a well in the centre and pour in the whisked eggs.
Bring the dough together using your hands.
Turn the pastry out on to a tapioca floured work surface and knead for about two minutes until the dough comes together into a smooth ball which is no longer sticky.
Flatten the ball slightly to make a thick round disc. Wrap in baking parchment and place in the fridge for 1 hour to chill before rolling out.
Pre-heat the oven to 190°C / 170°C fan assisted / gas mark 5 / 375°F.
Cut two large pieces of baking parchment, 21⁄2 inches wider than the size you need to roll the pastry out to.
Sprinkle tapioca flour on the inside of the parchment and place the chilled pastry disc between the parchment sheets.
Using a long rolling pin roll out the pastry into a round until it is about 5mm thick.
Peel away the baking parchment and use the rolling pin to lift the pastry over the baking tin.
Fit the pastry into the baking tin, patching up any cracking with excess pastry.
Use a sharp knife to cut away the excess pastry against the top of the tin.
Place in the fridge to chill whilst you prepare the frangipane.