Cube the butter and put it back in the fridge (or freezer for 10 minutes) while you measure everything else. It needs to stay cold through the whole process.
In the bowl of a food processor, combine the flour, salt, and sugar. Pulse a few times, just until mixed.
Add the cold butter cubes. Pulse in short bursts, 4 to 6 pulses at a time, until the mixture looks like coarse sand with some pea-sized pieces of butter still visible. Don't overdo it here. Those butter pieces are what give you flaky layers.
With the processor running on low, slowly pour in the ice water a couple tablespoons at a time through the feed tube. Stop and check after ½ cup. The dough is ready when it starts to clump together and holds its shape when you pinch it. You may not need the full ⅔ cup, depending on humidity.
Turn the dough out onto a clean surface. Divide it in half and shape each half into a flat disc. Wrap each in plastic wrap.
Refrigerate for at least 1 hour, or up to 2 days. This lets the gluten relax and the butter firm back up, both of which make the dough easier to roll and the crust more tender.
When ready to bake, roll out one disc on a lightly floured surface to about a 12-inch circle. Transfer to your pie dish. Cut, fold, and crimp the edges as desired. Repeat if you're making two pies or roll out for a top crust, if your recipe calls for it.