This hearty dish is traditional in the Czech Republic, and probably the simplest to make of all their soups. It is believed to be a remedy for the common cold as well as an excellent cure for a hangover.
Put the potatoes into a large pan with 1.5 litres/2½ pints/6¼ cups water, together with 5ml/1 tsp salt and the caraway. Bring the pan to the boil and cook for 15-20 minutes, or until the potatoes are soft.
Add the stock cubes and butter, then simmer for 2 minutes. Pour the egg into the soup and leave to cook for 2 minutes.