For pastry shell, mix flour, salt, and sugar in a food processor fitted with steel blade. Scatter butter over dry ingredients; process until mixture resembles cornmeal, 7 to 12 seconds. Turn mixture into a medium-sized bowl.
Drizzle 3 tablespoons of water over flour mixture. With blade side of a rubber spatula, cut mixture into little balls. Then press down on mixture with broad side of spatula so balls stick together in large clumps. If dough resists gathering, sprinkle remaining water over dry, crumbly patches and press a few more times. Form dough into a ball with your hands; wrap in plastic, then flatten into a 4-inch disk. Refrigerate for at least 30 minutes. (Can be refrigerated for 2 days or, if sealed airtight in a plastic bag, frozen for up to 6 months.)
Generously sprinkle a 2-foot square work area with flour. Remove dough from wrapping and place disk in center; dust top with flour. (If it has been chilled for more than 1 hour, let dough stand until it gives slightly when pressed, 5 to 10 minutes.) Roll dough in all directions, from center to edges, rotating a quarter turn and strewing flour underneath as necessary after each stroke. Flip disk over when it is 9 inches in diameter and continue to roll (but don’t rotate) in all directions, until it is 13 to 14 inches in diameter and just under ⅛-inch thick.
Fold dough in quarters and place the corner in the center of a Pyrex pie pan measuring 9- to 9 ½-inches across top. Carefully unfold dough to cover pan completely, with excess dough draped over pan lip. With one hand, pick up edges of dough; use index finger of other hand to press dough around pan bottom. Use your fingertips to press dough against pan walls. Trim dough overhanging the pan to an even ½-inch all around.
Tuck overhanging dough back under itself so folded edge is flush with edge of pan lip. Press double layer of dough with your fingers to seal, then bend up at a 90-degree angle and flute by pressing thumb and index finger about ½-inch apart against outside edge of dough, then using index finger (or knuckle) of other hand to poke a dent through the space. Repeat procedure all the way around.
Refrigerate for 20 minutes (or freeze for 5 minutes) to firm dough shell. Using a table fork, prick bottom and sides — including where they meet — at ½-inch intervals. Flatten a 12-inch square of aluminum foil inside shell, pressing it flush against corners, sides, and over rim. Prick foil bottom in about a dozen places with a fork. Chill shell for at least 30 minutes (preferably an hour or more), to allow dough to relax.
Adjust an oven rack to lowest position, and heat oven to 400 degrees. (Start preparing filling when you put shell into oven.) Bake 15 minutes, pressing down on foil with mitt-protected hands to flatten any puffs. Remove foil and bake shell for 8 to 10 minutes longer, or until interior just begins to color.