The key to getting a flaky pie crust without the addition of shortening or any chemical cheats is a french technique known as fraisage. It is used to blend the dough after all the ingredients have been cut together. Traditionally, it is performed by using the heel of your hand to smear the dough little by little across a floured board. Blending the dough together in this way that creates long alternating strands of butter and dough. As the crust bakes, any moisture turns to steam and expands to form pockets between the layers.
Using fraisage also makes a good crust for free-form tarts where leaking might be a concern. Because you are creating alternating layers of butter and dough, you are less likely to get a clump of butter that will melt during baking and form a hole in your crust as it bakes.
Instead of using your hand, you can use a dough scraper, or transfer the dough to a bowl and use a rubber spatula against the sides of the bowl. The important things to be aware of are not to overwork the dough or let the butter get too warm and melt. Just work quickly and gather up the layers of dough into a disc (or two for a double pie crust) and wrap them in plastic. Refrigerate for at least 30 minutes before rolling.
Try it! Use fraisage to make these recipes: