Place flour and salt in a large mixing bowl. Cut unsalted butter into cubes. Add butter and shortening to the flour. With your hands or a pastry knife, combine butter and shortening into the flour. It should combine with clumps being approximately the size of a marble. Next beat the egg and add to dough mixture. After the egg is combined add in apple cider vinegar and apple juice. The dough should be sticky but should not gum up your hands. Once completed, place dough in a Ziploc bag and let sit in the fridge for 1-2 hours.