Sift flour into a large mixing bowl. Add egg, salt and water to mix. Knead into a smooth dough. Divide the dough into small equal portions and shape each into a round ball. Flatten it with the palm of your hand and wrap each piece with cling film. Leave aside to rest for 4-8 hours.
To use the dough: Press out each piece of dough with the palm of your hands. Tear off a small piece of dough and pull it like a torn piece of paper-thin dough. Drop the torn pieces into boiling water. Cook until they start to float and are cooked through. Remove with a slotted spoon and drop them into a basin of iced water for a short while until cool. Drain and use in your soup base.