Place all ingredients except the soda and sugar in a mixing glass and stir well. Strain into a 6-ounce glass. Fill with soda water. Wet a spoon, dip it in sugar and stir into the cocktail.
Originally called omelette à la neige (snow omelet) in reference to the fluffy snow-like appearance of the meringue, île flottante (floating island) has a lengthy history that dates back to the 17th century.