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. The mixture does not need to resemble breadcrumbs. It’s okay that the butter is still in largish pieces. It should look quite shaggy in the flour.
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 during the blind bake.
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 / gas mark 5.
Cut two large pieces of baking parchment, 2½ 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 the baking tin in the freezer for 10 minutes.
Remove and place a sheet of baking parchment over the pastry and fill the tin with baking beans.
Place the baking tin on a large baking tray to help get it in and out of the oven.
Place the baking tray with the tin in the middle of the oven and bake for 25 minutes.
Remove from the oven and discard the parchment and baking beans.
Take the saved egg yolk from making the pastry and whisk it lightly in a small bowl. Using a pastry brush, brush the egg yolk all over the surface of the pastry and up the insides and on the edges.
Place back in the oven for 5 minutes.
Remove from the oven and let rest for a few minutes whilst preparing the filling.