Preheat the oven to 200C.
Using a electric beater, whisk together egg and sugar till light and creamy. Add flour, orange zest and vanilla while taking care not to collapse the batter
In greased mini tart moulds, add about 1 tbsp of batter each.
Bake in the pre heated oven for 8-10 minutes. Set aside for cooling
Once cool, demould and slice the cake in two thin halves horizontally.
In a heavy bottom saucepan, gently heat the orange marmalade till it is slightly melted and spreadable. Pour one tsp in the middle of the cut cakes
In the microwave or double boiler, melt together chocolate, water and orange zest. Pour over the orange marmalade and set aside for setting for 5 minutes and then pop the whole thing in your mouth for a medley of flavours.