From America's Test Kitchen Season 1: Holiday Pies
Basic pie dough often contains vegetable shortening, which makes the dough easier to handle and yields a crust that is remarkably flaky. The primary issue with vegetable shortening crusts, however, is that they lack flavor. We set out to master basic pie dough by determining the right fat, the right proportion of fat to flour, and the right method for combining them.
Flakiness is important to a crust, but so is flavor—and nothing beats butter. We experimented with a variety of combinations and ultimately settled on a proportion of 4 parts butter to 3 parts shortening as optimal for both flavor and texture. This crust is relatively high in fat, but we found that the proportion of flour to fat produces dough that is easier to work and a baked crust that is more tender and flavorful than any other. You can make this pie dough by hand, but the food processor is faster and easier and does the best job of cutting the fat into the flour.
For an 8- or 9-inch single pie shell