Makes one large rustic tart (galette! crostata!) that serves 8 people. Watch the short video above for some dough-making protips.
Place the flours into the bowl of a food processor fitted with the blade. Add the butter and pulse until the mixture resembles coarse sand with some larger pea-sized pieces.
Add 2 tablespoons of the water and process for a moment. Test to see if the dough holds together when you squeeze a bit with your hand. If not, add the remaining water and process again.
Use your hands to quickly form the dough into a ball. Then flatten into a disk between two approximately 14-inch square pieces of parchment paper. Wrap in the parchment and refrigerate for at least an hour (up to 2 days) before proceeding. //
Remove dough from fridge about 20 minutes before you want to roll it out. Usually it's fine to pull the dough from the fridge when you start to gather the ingredients for your tart filling.
Sprinkle a little bit of flour on each side of the dough and then replace the parchment. Using a rolling pin and turning the dough a quarter-turn clockwise every so often, roll the dough out between the parchment into a 14-inch circle (which should be about the same size as the parchment sheets themselves. Remove the top sheet of parchment and slide the dough (still on the bottom sheet of parchment) onto a pizza pan or baking sheet.