In the bottom of a large bowl, combine the flour, sugar and salt. Add the diced butter and using a pastry blender or your fingertips, work the butter into the flour until the mixture looks like coarse cornmeal, with the largest pieces the size of small peas. Add the egg, vanilla, and water, and if using a pastry blender, use that to work them into the butter-flour mixture, or if not, use a fork to work it in. Reach hands into bowl and lightly knead the mixture together into a single mass. Transfer to a piece of parchment or waxed paper or plastic wrap, and wrap it tightly. Chill in fridge until firm, at least 60 minutes.