Bring the stock to the boil in a large pan. Add the com, crabmeat, seasoning and soy sauce. Allow to simmer for 4-5 minutes.
Mix the cornstarch and water or stock and add a spoonful of the hot soup. Return the mixture to the soup and bring back to the boil. Cook until the soup thickens.
Whisk the egg whites until soft peaks form. Stir into the hot soup just before serving.
Slice the onions thinly on the diagonal and scatter over the top to serve.
Adding the egg whites is optional.
Do not allow the com and the crab to boil rapidly; they will both toughen.
Use crab sticks instead of crabmeat.
Chicken may be used instead of the crabmeat and the cooking time increased to 10-12 minutes.