In a large mixing bowl, combine flour, salt, and sugar. Mix well, then cut in shortening until mixture resembles coarse meal.
In a small bowl, combine egg, vinegar, and 4 tablespoons of water. Whisk together, then add gradually to flour mixture, stirring with a fork. Mix until dough forms a ball. Add one more tablespoon of water if necessary.
Allow dough to rest in refrigerator 10 minutes before rolling out.