In a medium bowl, stir together the flour and salt. Use a pastry blender to cut in the lard, until it resembles small peas. Using a fork, lightly stir in the egg and vinegar. If the dough does not stick together enough to pull away from the sides of the bowl, stir in a little cold water, about 1 teaspoon at a time. Form dough into a ball, wrap in plastic wrap, and refrigerate for at least 30 minutes before using.