In a food processor add flour, sugar and salt. Add well-chilled butter and well-chilled shortening. Pulse this for 3 to 4 times for 2 to 3 seconds each time, until it's crumbly.
In a small bowl blend egg yolk and water. Sprinkle this mixture evenly over the flour mixture in the food processor and 2 to 4 times, for 2 to 3 seconds each time, until the mixture pulls away from the sides of the bowl and clings together.
Now remove the dough, cover and chill for 1/2 an hour.
Flour work surface and rolling pin when working the dough. Roll to desired size.