Dissolve the sugar in the water and boil to 220 degrees Fahrenheit, until it reaches a syrup stage.
Take a little of the syrup and drop it slowly in cold water to test its readiness. The sugar should drop out from the spoon into threads when it has reached 220 degrees. As more water evaporates and the temperature gets higher, the syrup dropped into the water should resemble dark pearls.
Remove from heat at this point.
Beat the egg white until hard peaks form.
Add the hot sugar syrup to the white of egg, beating constantly.
Add the baking powder.
When the icing starts to foam, spread on your cake.