Use your hands to scoop up handfuls of the butter and flour mixture. Then with your palms facing up towards your face, use your thumbs to firmly rub the mixture upwards across the tips of your fingers. In a rapid fluttering motion, repeat this movement, flattening and breaking the butter into smaller bits. Continue this motion, letting the shaggy bits of this mixture continually fall back into the bowl as you gradually incorporate the butter into the flour.
When the mixture appears pale yellow, coarse, and all of the butter has been reduced to bits roughly no larger than pistachios, it is ready for the next step. (Another clue that the mixture is sufficiently incorporated is when you can actually begin to smell the butter.)
Add about ¼ cup of the ice water to start, drizzling it evenly over the mixture, and begin gently tossing everything together with your hands.
As the mixture starts to cohere, begin to press it together with your hands. If it doesn't seem to be sticking together, just gradually add more ice water until it does. (Up to about ½ cup total.) When the mixture starts to adhere into larger clumps, gather and press them together into a ball
For a double crust pie, divide the ball of dough into two pieces, making sure one is a bit larger than the other. (For two single crust pies, divide the dough evenly in half.) Press each piece of dough into a fat disk and wrap tightly in plastic. Refrigerate for at least an hour before rolling out and baking the dough.