In the bowl of a mixer fitted with a paddle attachment, combine the flour, salt, and sugar. Mix for 1 minute. Add the butter and mix just until the mixture resembles coarse crumbs. Stir the water and vinegar together, then gradually add to the flour mixture. Mix at medium speed just until a dough forms. Do not over-mix.
Divide the dough in 2 and shape into round, flat disks on sheets of waxed paper. Wrap separately and refrigerate for 30 minutes. On a lightly floured surface, roll the dough with a lightly floured rolling pin into a large circle about 1/8-inch thick. Place your pie plate upside down on top and trim with a sharp knife, leaving about 2 inches extra dough all the way around. Roll the dough circle up onto your rolling pin, then unroll it into the pie plate; or, fold into quarters, transfer to the pie plate, and unfold. Gently press the crust into place, turning any excess dough hanging over underneath to create a thicker edge. Press the edge with the back of a fork to create a decorative edge. Repeat with the other piecrust and leave covered for 30 more minutes.
Preheat the oven to 375 degrees F. Line each crust with a sheet of regular-weight aluminum foil, then pour in about 3/4 pound dried beans or pie weights. Bake the crusts 25 to 30 minutes, just until dry and set - then remove the foil and beans. Bake another 10 to 15 minutes or until golden brown, checking frequently to prevent over-baking. Remove from the oven immediately and let cool on wire racks.
Banana Cream Filling: Combine the milk, salt, and vanilla bean in a non-aluminum pan and heat, stirring occasionally. As soon as the mixture begins to boil, turn off the heat and stir the mixture for 1 minute. Whisk the egg yolks and sugar together until thick and pale yellow, then gradually whisk in the cornstarch. Gradually whisk in half of the hot milk mixture.
Pour the yolk-milk mixture back into the saucepan with the milk mixture and cook, whisking frequently, until the mixture boils and begins to thicken. Reduce the heat to medium-low and cook, stirring, about 5 minutes more, until the mixture no longer tastes starchy. The mixture should become very thick, like a set custard. When cooked, turn off the heat. Stir in the butter until it melts completely and fold in the bananas.
Pour the filling into the pre-baked pie shells. Push the banana slices below the surface to prevent them from browning, then smooth the tops. Cover with plastic wrap, gently pressing the plastic wrap against the surface to prevent a skin from forming. Refrigerate at least 7 hours or overnight, and serve with whipped cream.
Recipe courtesy Gale Gand, "American Brasserie" by Gale Gand, Rick Tramonto, Julia Moskin: Clarkson N. Potter Publishers, 1999