Whisk together flour, sugar, and salt in a bowl, then blend in butter with your fingertips or a pastry blender (or pulse in a food processor) just until most of mixture resembles coarse meal with small (roughly pea-size) butter lumps. Drizzle evenly with 9 tablespoons ice water and gently stir with a fork (or pulse in food processor) until incorporated. Squeeze a small handful: If it doesn't hold together, add more ice water 1 tablespoon at a time, stirring (or pulsing) until just incorporated, then test again. (Do not overwork mixture, or pastry will be tough.)