Stir sugar, vinegar, and 2 Tbsp. hot water in a small measuring glass to dissolve sugar. Add 1/3 cup ice water and stir to melt ice; chill in freezer until very cold, about 10 minutes (do not let it freeze). Pulse flour, butter, and salt in a food processor until largest pieces of butter are pea-size. Turn out onto a work surface and, using the heel of your hand, smash butter into flour to flatten. Working quickly, continue smashing butter into flour until mixture is pale yellow and resembles coarse meal. Gather into a mound and make a well in the center. Pour in sugar mixture, using your fingertips to slowly incorporate into flour; work in until only a few dry spots remain. Knead until no dry spots remain and dough holds together when pressed. Divide dough in half, flatten into disks, and wrap each in plastic. Chill until firm, at least 2 hours. Dough can be made 3 days ahead. Keep chilled, or freeze up to 1 month.