process flour, salt and sugar in food processor until mixed, about 3 seconds. Add butter and pulse until butter is size of large pieces, about ten 1-second pulses.
Using fork, mix sour cream and 1/3 cup ice water in small bowl until mixed. Add half of sour cream mixture to flour mixture; pulse for three 1-second pulses. Repeat with remaining sour cream mixture. Pinch dough with finger; if dough is floury and dry and does not hold together, add 1 to 2 tablespoons ice water and process until dough forms large clumps and no dried flour remains, 3 to 5 one second pulses.
Turn dough onto floured counter. Divide dough into two balls and flatten each ball into 4 inch disk; wrap each disc in plastic wrap and refrigerate until firm but not hard, one or two hours, before rolling out
If preparing the pastry in a warm kitchen, refrigerate all of the ingredients for 30 minutes before preparing the recipe to help keep the dough cool during preparation.