The Food Lab: The Science of Pie Dough
from http://sweets.seriouseats.com/

On paper, a classic American pie crust is a mind-bogglingly simple recipe. The underlying difficulty in the technique comes during the first stage of cutting the butter into the flour. It's simply impossible to accurately cut butter into flour to the same degree on a consistent basis. Don't cut it in quite enough, and you need to add extra water to absorb the excess dry flour, resulting in the over-formation of gluten, and a tough, leathery crust. On the other hand, cut it just bit too far, and you end up with way too little dry flour. Rather than having well-structured flaky layers, you end up with a crust that crumbles into sandy pieces.

This is the reason why you sometimes need to add a couple tablespoons of water and other times up to twice as much to get the dough to come together—it's got nothing to do with the relative humidity of the air as many books will have you believe.

As you add butter and it beomes coated with flour, and a fat/flour paste forms at the interface between the pure fat and the dry flour. With this paste, what you're getting is essentially single particles of flour that are completely coated in fat. Since they can't absorb any water, they end up behaving in much the same way as pure fat.

To summarize, here's what we've got as we're forming a pie dough: Dry flour, completely uncoated by fat, that absorbs water when you add it, forming gluten that then gets stretched out into wide layers. Pure pockets of fat that will flatten out into long, wide, thin sheets as you roll out your dough, separating the layers of gluten-enforced flour from each other so that rather than forming a solid, leathery mass, they separate and gently puff as they bake. A flour/fat paste that functions much in the same way as pure fat does. As it bakes, the fat melts and a tiny amount of individually separated flour bits will deposit themselves and become incorporated into the gluten-enforced layers.

In order to get a flaky crust, all you have to do is add some extra plain dry flour to a fat/flour paste, pulse it a couple times in the food processor just to distribute it evenly, then proceed just like an normal pie crust: Add water, chill it, roll it, and bake it.

By measuring out a given amount of flour and fat and combining them together until they form a near homogeneous paste and then adding the remaining dry flour to that paste, you are very strictly defining exactly how much flour is used for gluten formation and how much ends up coated with fat. No more trying to visually judge whether your fat is properly cut. No more adding ice water a drop at a time until a dough is formed. The dough comes out the same, every single time.

The other key advantage is that your dough becomes much more pliable. The fat/flour paste formed at the beginning is much softer and more malleable than pure butter is, which means that your final dough rolls out smoothly and easily with little to no risk of cracking like a traditional pie crust.

Butter, Shortening, or Lard

Which fat makes the best crusts is prime stomping grounds for eternal debate between bakers, and it comes down to a battle between texture and flavor.

Butter:

Pros: Excellent flavor, forms distinct, large flaky layers.

Cons: Difficult to work with. Butter melts at a relatively low temperature (below body temperature) and has a very narrow workable range. It's also got a relatively high water content (about 15 to 17 percent), which can cause excess gluten to form and turn your crust leathery if you aren't careful.

Shortening:

Pros: Very easy to work with, produces crusts that are extremely tender.

Cons: It has no flavor at all other than grease. It's also soft over a wide range of temperatures, greatly increasing your chance of overworking your dough and turning it crumbly instead of flaky.

Lard:

Pros: The best for working with—it has a wide workable temperature range and is not nearly as soft as shortening within that range. Creates very tender, flaky crusts.

Cons: Unless you slaughter your own pigs and render your own leaf lard, it's extremely hard to find good lard.

Easy Pie Dough

2 1/2 cups (12.5 ounces) all-purpose flour
2 tablespoons sugar
1 teaspoon kosher salt
2 1/2 sticks (20 tablespoons) unsalted butter, cut into 1/4-inch pats
6 tablespoons cold water

Combine two thirds of flour with sugar and salt in the bowl of a food processor. Pulse twice to incorporate. Spread butter chunks evenly over surface. Pulse until no dry flour remains and dough just begins to collect in clumps, about 25 short pulses. Use a rubber spatula to spread the dough evenly around the bowl of the food processor. Sprinkle with remaining flour and pulse until dough is just barely broken up, about 5 short pulses. Transfer dough to a large bowl.

Sprinkle with water then using a rubber spatula, fold and press dough until it comes together into a ball. Divide ball in half. Form each half into a 4-inch disk. Wrap tightly in plastic and refrigerate for at least 2 hours before rolling and baking.

Pie dough can be frozen for up to 3 months. Thaw in refrigerator before rolling and baking.

YIELD: Makes 2 single crust or 1 double crusted pie