Preheat the oven to 180c and grease and line a swiss roll tray/rectangle baking tray with baking parchment so some comes over each end - You will need this to pick it up with when it is just out of the oven
Melt the chocolate either in a glass bowl over a pan of boiling water (Do not let it touch the water) or at 10 second intervals in the microwave - When melted, allow to cool.
Whisk the egg whites until they make soft peaks
Add the sugar to the egg yolks and whisk together until pale and start to thicken
Add the zest of two of the oranges or 1 tsp of the orange extract to the egg/sugar mixture
When the chocolate has cooled enough, add it to the egg yolk mixture. Make sure it is definitely cool enough - you don't want to scramble the eggs.
Add the egg whites to the rest of the mixture
Bake for 25-30 minutes
As soon as the cake comes out of the oven, remove from the tin. The baking parchment will still be attached which is fine.
Bend the cake as if you are rolling it while it is still hot and malleable
While you are allowing the cake to cool for approx 10 minutes, whisk the pot of cream until it is thick enough to spread and stay put. You don't want it too solid.
Spread a thin layer of marmalade over the inner surface of the cake and spread the cream on top
Roll up the swiss roll and sprinkle lightly with icing sugar