In a large bowl, whisk together the flour, cocoa powder, and salt. Add the cubed butter, tossing the cubes through the flour until each individual piece is well coated. ‘Cut’ the butter into the flour by pressing the pieces between your fingers, flattening the cubes into big shards. As you work, continue to toss the butter through the flour, recoating the shingled pieces.
For a flaky crust, continue cutting the butter into the flour just until the pieces of butter are about the size of walnut halves. Or, for a mealy crust, continue to work the mixture together until the pieces of butter are about the size of peas.
Make a well in the center of the flour mixture. Add the amount of ice water listed in the recipe to the well, but have more on hand. Use a tossing motion with your hands to start to mix the two together (this begins to combine them without creating too much gluten). As it begins to become hydrated, you can start to use more of a kneading motion – but don’t overdo it: this will make the dough tough. Add more water about 1 tablespoon at a time until the dough is properly hydrated: it should be uniformly combined and hold together easily, but it won’t look totally smooth. Dough that is too dry may have sort of a “dusty” appearance, or pockets of un-hydrated flour. It will not hold together and will appear crumbly. Dough that is too wet will feel sticky or tacky to the touch, and is often smoother and/or lighter in color.
Form the dough into an even disk (or into another shape if directed by the recipe – or if you are multiplying the recipe to make multiple crusts, divide the dough appropriately). Wrap tightly in plastic wrap and refrigerate for at least 30 minutes and up to 2 days.