In a food processor, pulse together the flour, sugar and salt. Add the butter and shortening and pulse until the pieces are the size of small peas. Drizzle in 2 1/2 tablespoons of the ice water and pulse a few times, adding a little more water if necessary until the dough can be gathered into a ball. Pat the dough into a 6-inch disk. Wrap it in plastic wrap or wax paper and refrigerate for at least 1 hour or overnight. Let the dough soften at room temperature for 5 minutes before rolling out.