Beat egg white with sugar over boiling water for seven minutes until thick enough to spread.

Steps

1. Put all ingredients except baking powder and vanilla in double boiler on stove and beat over boiling water with an egg beater for seven minutes or until thick enough to spread on cake.
2. Remove from heat; beat in baking powder and vanilla.
3. Spread on cake. Icing will take longer to thicken on wet days.