To make the galette dough: Place flour and salt in the bowl of a food processor. Pulse for a few times to mix. Add in the cold butter cubes. Pulse 8-10 times until butter resembles small clumps.
Turn the machine on and add in 4 tablespoons of ice-cold water in one tablespoon increments.
At this point, it should start to come together and form into a ball. If not add in the rest of the water until it does.
Transfer onto a lightly floured surface, form it into a 4-inch disk, and wrap with plastic. Place in the fridge for at least 1 hour or overnight.
Take it out of the fridge 10 minutes before you are ready to roll it out.
Lightly flour your working surface. Roll the dough into a large 12-inch circle. Transfer onto the parchment paper and then onto the baking sheet.
Place your filling (depending on the recipe you are using) on top slightly mounting in the middle, leaving a 3-inch border around the edges.
Roll the sides of the dough overlapping as you go around and pleating the dough.
Brush the edges of the dough (the outer crust) with egg yolk.
Bake according to the instructions of the recipe you are using.