Add the flour and salt to a large bowl and stir to combine. Add the butter and toss to combine. With your fingers, begin to "smush" the butter into flat pieces. Continue smushing until all the butter is flattened but none of the pieces are larger than a quarter. The flour will look like coarse cornmeal.
Add the water, quickly folding it in with a wooden spoon to distribute the moisture. (Do not stir vigorously--the dough should appear shaggy.) Use your hands to break up any large clumps of moisture. Then use your knuckles or a palm to smear the dough up the sides of the bowl (a technique known as fraisage). This distributes the butter over a larger surface to achieve larger flakes and compact the dough. Once you've gone around the bowl one time, fold the dough over itself a few times to pick up any dry bits from the bottom. Gently press the dough into a disk. (Note: The dough should remain very cool to the touch throughout the process. If it approaches room temperature, refrigerate it for 5 to 10 minutes to chill.)
Transfer the dough to a lightly floured work surface and roll out to a 10-by-12-inch rectangle. Perform a letter fold by folding one of the short ends towards the middle and the other short end over the first, like folding a business letter.
Turn the dough 90 degrees, so the long side faces you, and perform a second letter fold. Turn the dough 90 degrees again; perform a third letter fold.
If the dough still feels cool, it can be used immediately. Otherwise, wrap it in plastic wrap and chill for at least 20 minutes. The dough can be refrigerated for up to 1 week or frozen for up to 1 month.