In a food processor, combine the flour, sugar and salt. Pulse until just blended. Add the butter and shortening and pulse a few times, until it forms pea-size pieces. Add 1/4 cup (60 ml) ice water and pulse just until the dough starts coming together. Add more water as needed. Remove the dough from the food processor and form into two discs. Wrap each disc in plastic wrap and refrigerate for one hour.