You’ll need about 95 grams (appx 1 cup) cold-as-possible-without-being- frozen-butter. Cut it up into small pieces and then put it back into the fridge to chill from the cutting.
The goal here is for the flour to “host” the butter-- incorporated but still distinct. When this dough hits the hot oven, the fat particles will grab hold of the flour and burst-- this leaves you with a flaky, buttery crust.
Add in the flour, the salt and the very-cold-butter.
Pulse in the processor until it starts to resemble cornmeal.
Make a well. In another bowl, whisk together the egg yolk and the water, and then pour it into the mixer. Begin to pulse until it becomes a dough.
Wrap in cellophane and slide into the fridge.
In a bowl, mix together the flours and the salt, and turn it out onto a cold surface (like a pastry slab or countertop), and make a well in the center.
In another bowl, whisk together the egg yolk and the water.
Put the very-cold-butter in the middle.
Start to chop the butter into small pieces with a dough cutter.
Pour in the yolk-water mixture. Begin to chop them both into the flour, compiling them into one heap.
Use one hand and push the dough away from you at an angle, and chop-chop-chop all the way back. Don’t use too much force as you knead-- you’ll make the dough tougher.
Gently knead once the butter is incorporated.
...till you arrive at one uniform ball.
Wrap it in cellophane and let it cool and rest in the fridge for a few hours.