1. Cut butter into 1/2-inch (1 cm) cubes; set aside 3/4 cup (175 mL) in refrigerator. In food processor, blend flour with salt. Sprinkle remaining butter over top; pulse until indistinguishable, about 10 seconds. Sprinkle with reserved butter; pulse 4 or 5 times to cut into pea-size pieces. 

2. Pour water evenly over mixture (not through feed tube). Pulse 6 to 8 times until loose ragged dough forms (do not let form ball). Transfer to floured waxed paper; gather and press into rectangle. Dust with flour; top with waxed paper. Roll out into 15- x 12-inch (38 x 30 cm) rectangle. 

3. Remove top paper. Starting at long edge and using bottom paper to lift pastry, fold over one-third; fold opposite long edge over top, bringing flush with edge of first fold to make 15- x 4-inch (38 x 10 cm) rectangle. Starting from 1 short end, roll up firmly; flatten into 5-inch (12 cm) square. Wrap and refrigerate until firm, about 1 hour. (Make-ahead: Refrigerate for up to 5 days or freeze in airtight container for up to 2 weeks.)