Stir together the flour, sugar, and salt. Using a pastry cutter or a food processor (if I had one I would use it!), cut the shortening and butter into the flour until the mixture resembles coarse crumbs. It is only about 10 pulses with a food processor but a bit more work by hand. One trick to make the process a little easier is to freeze your butter beforehand, then grate it into the flour mixture before cutting it in with the pastry cutter if not using a food processor.