Place apricots in bowl, cover with hot water, leave until well plumped; then puree in electric blender or rub through sieve.
Place egg-whites and 1 tablespoon of the sugar in large mixing bowl, beat until thick and of meringue consistency.
Gradually beat in remaining sugar and apricot puree.
Grease souffle or ovenproof dish, dust lightly with extra castor sugar.
Pour in souffle mixture gently so air bubbles will not be broken down (a good way to do this is to pour it over back of spoon).
Bake in moderate oven, Mark 4, 350°F., 30 minutes.