If using a food processor, pulse the flour, sugar and salt a few times until combined. Add the butter pieces and pulse until the mixture resembles large peas. If making the pastry by hand, whisk the flour, sugar and salt together in a bowl and then cut in the butter with either a pastry blender or two knives.
Slowly add the ice water, 1 tablespoon at a time. In the food processor, pulse a few times; by hand, mix with a fork. Continue adding water 1 tablespoon at a time until the dough easily sticks together when you pinch a large piece. If it crumbles, add more ice water but not so much that the dough becomes sticky.
Turn the dough out onto a lightly floured work surface and form into a ball. Cut in half. Without overworking the dough, form each half into a rough ball and flatten each ball into a disk. Place each disk on a plate and invert another plate over it. Chill the dough for at least 1 hour in the refrigerator or 20 minutes in the freezer.