Step 1 To make the dough using a food processor, pulse together the flour, salt and sugar until thoroughly combined. Add the shortening and pulse until incorporated (the dough will look like moist sand). Add the butter and pulse just until the butter is reduced to pea-sized pieces. Sprinkle the vinegar and 4 tablespoons water over the mixture, and pulse a few times to form the dough, then a few more times just until the dough begins to clump together to form a cohesive dough. If the dough is too crumbly and dry, pulse in additional water, 1 tablespoon at a time. Remove the dough and mold it into a disk roughly 6 to 8 inches in diameter. Cover the disk tightly with plastic wrap and refrigerate at least 2 hours, preferably overnight.
Step 2 Alternatively, to make the dough by hand, whisk together the flour, salt and sugar in a large bowl. Add the shortening and incorporate using a pastry cutter or fork (the dough will look like moist sand). Cut in the butter just until it is reduced to pea-sized pieces. Sprinkle the vinegar and 4 tablespoons water over the mixture, and stir together until the ingredients are combined to form a dough. Remove the dough to a lightly floured surface and knead a few times until it comes together in a single mass. If the dough is too crumbly and dry, gently work in additional water, 1 tablespoon at a time. Mold the dough into a disk roughly 6 to 8 inches in diameter. Cover the disk tightly with plastic wrap and refrigerate at least 2 hours, preferably overnight.