Ingredients
There are three basic ingredients in a pie crust, fat, flour and liquid. You can come up with numerous variations just by changing your basic ingredients and their ratios.
Flour:
To promote tenderness in your pie crust, choose a low protein wheat flour such as cake flour or pastry flour. All-purpose flour is readily available and works pretty well for pie crusts. Unbleached flour is more tender. To make a pastry-type flour from all-purpose, put 1 tablespoon of cornstarch or other non-gluten flour in the bottom of the cup for every cup of flour you measure.
If you want to use a whole grain flour to make pie crust, allow extra time. You will have a much more tender crust if you refrigerate the pie dough overnight before baking to allow the bran to rehydrate thoroughly.
Fat:
The type of fat affects flavor and flakiness, while the amount affects tenderness. Flaky crusts result when bits of unmelted fat are layered between layers of flour and melt away with baking. They can be made from a variety of solid fats. Crusts made with all butter are very flavorful, but the milk solids and water in butter reduce the amount of fat compared to lard or vegetable shortening, so butter crusts usually are not as flaky as crusts made with shortening or lard. Vegetable shortening has much less cholesterol but more trans fats. It produces a flakier pie crust that is slightly easier to work with than one made with butter. Lard, a saturated fat, produces the flakiest crust and leaf lard or kidney fat is preferred for pastry. Some of the best pie crusts are made with a combination of fats, part butter for flavor and part shortening for flakiness and ease of workability.
You can also make a pie crust with vegetable oil. The resulting crust won't be as flaky as a solid fat crust, but it does make a very tender crust that almost melts in your mouth.
Liquid:
For a tender crust, you want just enough liquid to moisten the flour without drenching it. When adding liquid to the flour and fat mixture it must be ice cold in order not to melt any of the fat. Water is most common, but eggs, sour cream, cream cheese, and cream can also be used, adding different flavors and textures to your pie crust. Always add liquid a little bit at a time. If you add too much liquid your crust could turn out tough.
Acid ingredients like vinegar and sour cream prevent the flour from developing all its protein, making the crust a little more tender.
Techniques
These techniques will help you produce a tender, flaky crust every time.
Baking tips:
In a classic two-crust apple pie, the pastry is tender and flaky, and the fruit remains in separate pieces that aren't mushy. The apples in the pie hold together when cut and served. The juices are a thick, clear, silky syrup, achieved by using a small amount of cornstarch or tapioca flour as a thickener to complement the natural pectin in the apples. Minute Tapioca is more widely used, but tapioca flour produces a slightly smoother result than Minute Tapioca. If in doubt about the amount of thickener needed, remember a slightly runny pie is infinitely preferable to one whose filling resembles concrete. The cook lets the fruit pie cool completely and leaves it at room temperature for about 6 hours before serving, so that the filling can set up and not be runny.
A good sharp cheddar is wonderful with warm apple pie.