Soak the chicken breast in the ginger and sherry. In a large saucepan combine the chicken stock, corn and salt then bring to a boil. Stir in the chicken, ginger and sherry mixture. Simmer until chicken is cooked through.
Stir in the cornflour water mixture then stir until thickened. Stir in the egg whites. Remove from heat, stir in the oil and spring onion then serve.