In a small bowl or pitcher, measure ½ cup cold water and add the vinegar
Crack in the egg and whisk to combine. Place the pitcher in the freezer for a few minutes to ensure it's extra cold
While it's chilling, in a large bowl, whisk together the flour and salt
Add the butter and shortening and use a pastry blender or two knives to incorporate them into the dry ingredients. Keep going until the mixture is mostly smaller crumbs but still has a few pea-size bits of butter and shortening
Grab the pitcher from the freezer and slowly drizzle the egg mixture into the bowl, stirring gently to mix
Stir to bring everything together, adding up to 2 more tablespoons of cold water if the dough seems overly crumbly or dry
Pack the dough down a couple of times with the palm of your hand, then dump it out of the bowl
Pack it into a ball, gathering as many loose crumbs as you can, and cut it in half with a bench scraper or knife
Put each half into a gallon storage bag. Pat it into a disc, seal the bag, and freeze for 30 minutes before rolling out, or up to 4 months if you're using the crust later. When you're ready to use the frozen dough, thaw the discs overnight in the fridge if you have the time, or at room temperature for 1 hour, before rolling out
