Sift the self-raising flour and cornflour together twice. Mix the cocoa powder and water into paste.
Place egg whites in a large mixing bowl together with half the castor sugar and cream of tartar. Whisk until the mixture is stiff and holds its shape.
Whisk egg yolks, remaining sugar, salt, orange juice, essence and corn oil until light and thick. Add the sifted flours and continue to whisk until well combined and smooth.
Gently fold egg white mixture in 3-4 batches into the egg yolk mixture. When evenly blended, scoop out one ladleful of batter and add cocoa paste to it. Stir to mix until well blended. Leave aside.
To the remaining chiffon mixture, add orange rind and passion fruit pulp. Gently fold and mix well to combine.
Pour half portion of orange batter into an ungreased 22cm springform chiffon tube pan. Spoon half portion of cocoa flavoured batter over the orange batter. Top with remaining chiffon batter. Add the remaining cocoa batter over that. Use a satay skewer to swirl the cocoa batter to form a marble design.
Bake in a preheated oven at 180°C for 30-35 minutes or until a skewer inserted in the centre of the cake comes out clean.
Invert the pan and allow the cake to cool completely before easing it away from the sides of the pan with a palette knife.