Cut butter into 1/2-inch cubes and freeze for 10 minutes (not more).
You can mix with your hands or with a hand-held pastry blender, but I prefer a food processor for ease.
Process flour, salt and sugar together in food processor until combined, about 3 seconds. Add butter and pulse until butter is size of large peas, about ten one-second pulses.
Using fork, mix sour cream and 1/3 cup ice water in small bowl until combined. Add half of sour cream mixture to flour mixture; pulse for three 1-second pulses. Repeat with remaining sour cream mixture.
Pinch dough with fingers; if dough is floury, dry and does not hold together, add 1 to 2 tablespoons ice water (start with less), and process until dough forms large clumps and no dry flour remains, three to five 1-second pulses.
Divide dough into two balls and flatten each into 4-inch disk; wrap each disk in plastic and refrigerate until firm but not too hard, 1 to 2 hours, before rolling.
(Dough can be refrigerated for up to 24 hours. Let thoroughly chilled dough stand at room temperature for 15 minutes before rolling. Dough can also be frozen. I usually make at least one extra recipe's worth, form the dough into pie pans, then freeze for later use. Just thaw before using!).