For pastry 2 cups all-purpose flour 1 stick (1/2 cup) cold unsalted butter, cut into 1/2-inch cubes 1/4 cup vegetable shortening 1/2 teaspoon salt 4 to 5 tablespoons ice water For filling 4 bacon slices (1/4 lb), cut crosswise into 1/8- to 1/16-inch-wide strips 3 tablespoons unsalted butter 2 lb onions, halved lengthwise and very [...]