1.Pre-heat oven to 200°C. Grease six ovenproof souffle dishes (3/4-cup capacity). Sprinkle the bases and sides evenly with the caster sugar; shake away the excess. Place dishes on an oven tray.
2.Whisk 2 egg yolks (reserve remainder for another use) with passionfruit, rind and 2tbsp of the sifted icing sugar until combined.
3.Beat egg whites in a small bowl with an electric mixer until soft peaks form. Add remaining sifted icing sugar and continue beating until firm peaks form.
4.Fold a quarter of egg whites mixture into the passionfruit mixture, then gently fold in the remaining egg white mixture.
5.Spoon into prepared dishes and bake in a moderately hot oven, about 10 minutes, or until the souffles are well risen and browned. Dust the tops with extra sifted icing sugar, if desired.