Preheat the oven to 160?C (140?C). To make the cupcake mixture, first put the chocolate (broken up into pieces), the margarine, both types of sugar and the water in a large microwaveable bowl. Microwave in thirty second bursts, stirring each time, until everything is completely melted and smoothly combined.
Next, weigh out the flour and add to the chocolate mixture. Beat really well until there are no lumps left. Add the In A Pickle Christmas Morning Marmalade and stir well again.
Finally, break the eggs into the mixture one at a time, beating really well until completely combined.
Grease a muffin tray, and then fill each hole about half way up with the cupcake mixture. Place in the oven and bake for 35 minutes.
Allow the cupcakes to cool in the tin for about ten minutes, then gently loosen each one with a knife round the edge, and carefully take out ? they?ll be quite delicate, so go slowly. Place them upside down on a wire rack (they should have fairly flat tops, and the bottoms will be especially delicate) to cool.
Once the cupcakes are completely cold, you can ice them. Beat together the margarine and icing sugar until smooth, then add a little red and yellow gel food colouring (much better than the water-based stuff, which can curdle your buttercream) and the orange essence (if using) and mix until you have the desired colour.
Pipe the buttercream onto the cupcakes with a star nozzle, and then finish each one with a slice of chocolate orange.