Sift the flour with the salt, and sugar if using, into a bowl. Add the butter and shortening and cut into small pieces with a pastry cutter or two knives, using one in each hand. Rub with your fingertips until the mixture forms fine crumbs, lifting and crumbling to help aerate it.
Make a well in the center of the mixture, add egg yolk if using, and water. Mix quickly with a knife to form crumbs. If they are dry, mix in 1-2tablespoons more water. Press the dough together with your fingers. It should be soft but not sticky.
Work the dough lightly with your hand for a few seconds to form a rough ball. Wrap it tightly in plastic wrap and chill in the refrigerator for 30 minutes or until it is firm. Knead and roll as for pâte brisée.