In a food processor, combine the flour, salt and sugar. Add the butter and shortening and pulse on and off about 20 times or until the mixture resembles coarse meal.
Add ¼ cup ice water and pulse to combine. Continue pulsing on and off until the dough begins to gather in a ball, adding a little more ice water, if necessary. Remove dough, wrap in plastic and refrigerate 30 minutes.
Preheat oven to 180°C / 350°F.
On a floured work surface, roll out dough and press into a 23 cm (9 inch) pie plate with removable bottom. Prick all over with a fork, cover with a sheet of aluminum foil and fill with dried peas or beans.
Bake on lower rack of oven for 25 minutes. Remove aluminum and peas and set aside to cool.
In a small saucepan, combine the lemon juice and zest, sugar, corn starch, egg yolks and melted butter. Cook until thick and pour into the cooled pie crust.
Bake on the lower rack for 20 minutes, remove from oven and cool at room temperature.