Melt
the butter in a saucepan, add the onions and cook for a few minutes. Add the
flour and cook for 1 minute. Stir in the stock or water; bring to the boil,
season with pinch of pepper, then simmer gently for 5 minutes. Grate the cheese.
Add to the soup and simmer until cheese is melted. DO NOT ALLOW TO BOIL.