Fit bowl of food processor with the metal blade; add in the flour, sugar, salt, and butter.
Process on/off for 10 seconds (ten 1 second pulses) until the mixture resembles coarse meal.
Add the egg and water to a small bowl; beat to mix.
Through the feed tube, add the egg/water mixture and continue to process briefly (about 20 seconds) only until the mixture barely (but not completely) holds together.
Turn mixture out onto a large unfloured board or smooth work surface; knead briefly (only a few seconds) until the mixture is smooth and holds together; press the mixture together to form a ball.
Smooth the sides and flour it lightly.
*Unless the kitchen is terribly hot, or unless you have handled the mixture too much (enough to melt the butter), it is not necessary to refrigerate this before using; if you must, refrigerate it for only about an hour or less; if it is refrigerated too long it will crack when you roll it out.