Place the flour and salt in the bowl of a food processor fitted with the steel blade. Cut the butter into slices, add to the processor, and buzz several times, until the mixture is uniform and resembles coarse meal. (If you don't have a food processor, use a pastry cutter or 2 forks instead.)
Continue to process in quick spurts as you add the water, 1 tablespoon at a time. As soon as the dough adheres to itself when pinched, stop adding water and turn the dough out onto a floured surface. Gather it gently into a ball.
Roll the dough into a circle 11 inches or so in diameter (slightly bigger than a 10-inch round). Lift the dough and ease it into a 9-inch pie pan or 10-inch springform tart pan, nudging it gently into the corners. Form a generous, even edge all the way around the sides. If you're not going to use the crust right away, wrap it tightly in plastic wrap and refrigerate or freeze.