stick cold unsalted butter, cut into 1/2-inch cubes
white wine vinegar
In a large bowl, whisk together the flour and salt. Add the cubed butter and cut in with a pastry cutter or two knives until it resembles coarse crumbs. In a small bowl, beat together the egg, water, and vinegar. Add it to the flour mixture, and stir until just combined. The mixture will look pretty rough and shaggy. Knead gently a couple times, just enough to bring the dough together. Wrap the dough in plastic, and refrigerate for at least 1 hour.