1) Whisk together the flour, salt, and buttermilk powder (if you're using it).
2) Dice the butter into small cubes, or cut it into pats. Work it into the flour until it's well-distributed, but not fully incorporated. Larger, pea-sized pieces of butter will be scattered throughout the mixture.
3) Tossing with a fork or your fingers, drizzle in the ice water. Stop adding water when the dough starts to come together, and grab it in your hands. If it holds together easily, without crumbling, it's ready. If it has dry spots, or pieces break off easily, add a bit more water until it's totally cohesive.
4) Gather the dough into a ball, and divide it in half. Gently pat/shape each half into a rough disk. Roll immediately, if desired. For better texture, chill the dough for at least 30 minutes before rolling. If dough has been refrigerated longer than 30 minutes, allow it to warm at room temperature for 10 to 15 minutes, until it rolls easily.
Yield: pastry for 1 double crust pie or 2 single crust pies.