To mix dough by hand, combine flour, salt and baking powder in a medium mixing bowl and stir well to mix. Cut butter into 1 tablespoon pieces and add to dry ingredients. Toss once or twice to coat pieces of butter. Using your hands or a pastry blender, rub the butter into the dry ingredients by breaking it into tiny pieces, continuously pinching and squeezing it into the dry ingredients. Be careful to keep the mixture uniform by occasionally reaching down to the bottom of the bowl and mixing all the ingredients evenly together. Continue rubbing the butter into the dry ingredients until the mixture resembles a coarse ground cornmeal and no large pieces of butter remain visible. Scatter the smaller amount of water on the butter and flour mixture and stir gently with a fork - the dough should begin holding together. If the mixture still appears dry and crumbly, add the remaining water, 1 teaspoon at a time, until the dough holds together easily.

To mix the dough in the food processor, combine flour, salt and baking powder in work bowl fitted with metal blade. Pulse 3 times at 1-second intervals to mix. Cut butter into 1-tablespoon pieces and add to work bowl. Process, pulsing repeatedly at 1-second intervals, until the mixture is fine and powdery, resembles a coarse ground cornmeal and no large pieces of butter remain visible, about 15 pulses in all. Scatter the smaller amount of water on the butter and flour mixture and pulse 5 or 6 times -the dough should begin holding together. If the mixture still appears dry and crumbly, add the remaining water, 1 teaspoon at a time, until the dough holds together easily.

Scrape the dough onto a lightly floured surface and form it into a disk (two equal disks for the larger amount of dough). Sandwich the disk of dough between two pieces of plastic wrap and press it into a 6-inch disk. Refrigerate the dough until firm, or until you are ready to use it, at least 1 hour.