Using a food processor, a chopping blade in a bowl, or cold fingers, work the cold fat into the flour and salt until it looks like corn meal.
Cautiously add just enough water to the mixture, while tossing it with a fork or butter knife, to allow you to clump it up in a ball. (This is the part where you really need to pay attention—the combination of sloshing in an excess of liquid and overmixing has been the ruin of many a piecrust.) Divide the ball with a knife into two uneven segments, one nearly twice the size of the other—i.e., ⅔ and ⅓ of the dough. Quickly press each into an even, flattish disc, wrap airtight, and chill.
At least an hour later, take the smaller dough section out. Use a floured rolling pin to roll it out evenly on a floured counter, aiming to make an oblong, not round, shape around ¼-inch thick. Working quickly and with a light touch, smear half the soft butter over ⅔ of the surface. (Imagine that it’s a business letter, and you’re leaving everything from the greeting line up butter-free.) Fold the unbuttered third of the pastry over the middle third, then the free third over that. (Yes, just like you’d fold a business letter; such a coincidence….) Very lightly roll it out a bit without extruding any butter, aiming for the business letter shape, but perhaps not as large as last time. Repeat the buttering and folding routine, just barely tapping it into cohesion with the rolling pin when you finish. You’ll have something more like a book than a ball of dough at this point. Wrap it back up and chill it for at least an hour, while you shuck your quahogs.