1) Whisk together the flour and salt.
2) Add the shortening, working it in until the mixture is evenly crumbly.
3) Add the butter to the flour mixture, and work it in roughly with your fingers, a pastry cutter, or a mixer. Don't be too thorough; the mixture should be very uneven, with big chunks of butter in among the smaller ones.
4) Add 2 tablespoons of water, and toss to combine.
5) Toss with enough additional water to make a chunky mixture. It should barely hold together when you squeeze a handful, though the remainder may look quite dry.
6) Scoop the mixture out onto a piece of parchment or waxed paper, and flatten it out a bit. Take a spray bottle of water, and spritz the dry parts with the water.
7) Using the parchment or waxed paper, fold the dough over on itself — first from one side, then from the other. You'll find that the dry crumbs are becoming incorporated with the cohesive dough. If there are still dry areas, spritz them with additional water, and fold the dough in on itself again. Keep folding and gathering until just a few dry crumbs remain unincorporated; this should only take a few folds. For a visual demonstration of this technique, see Pie, Any Way You Slice It.
8) Shape the dough into a disk about 1" thick, and refrigerate it for 30 minutes or longer; this resting period allows the flour to absorb the water, making the dough easier to roll out.
9) When you're "ready to roll," remove the dough from the fridge. If the dough has been refrigerated longer than 30 minutes, let it rest at room temperature for 10 to 15 minutes before rolling, to allow the butter to soften up a bit.
10) Roll the dough to the size needed (about 12" for a 9" pie). Fill and bake as directed in your recipe.
Yield: one crust for a single-crust pie.