Add the flours, salt, and butter to the bowl of a food processor or Thermomix.
Pulse 3 - 4 times, until the butter is cut into small chips. The butter should range from the size of a grain of rice to around the size of a small bean.
Tip the flour mixture into a large bowl.
Drizzle the cold water, starting with the lower amount, over the flour.
Using a butter knife, cut the water into the flour, until there is no dry flour visible. If dry areas remain, drizzle in a little more water and repeat the cutting action.
When all of the flour appears damp, tip the mixture onto a piece of cling wrap and pat into a 15cm round. Just gently press the dough. Do not try and work it at this point.
Wrap the pastry in the cling wrap and place in the fridge for at least 30 minutes. I often make this pastry the day before I wish to use it.
When you are ready to use the pastry, lightly flour the bench and the surface of the pastry.
Roll out the pastry to the desired thickness. The pastry should remain cold at all times or it will become sticky and difficult to work with. Continue to lightly dust the bench and the surface of the pastry as required, but try to limit the amount of flour used. If at any time the pastry starts to get sticky and difficult to roll, put it on a tray and place in the fridge or freezer until it feels cool to the touch.
Use as desired.