Line an 11x7 inch pan with two pieces of cling film, leaving about an inch of overhang on all sides. One piece should be horizontal, and the other piece vertical, creating handles that will aid in lifting the fudge out of the pan.
Combine all the ingredients ,except the orange zest, in a medium size bowl. Put the bowl over a pan of boiling water (a double boiler) and simmer until the mixture is glossy. *see notes
Stir in 2 teaspoon of orange zest, and quickly pour the fudge into the prepared pan.
Sprinkle the remainder of the zest over the top of the fudge and transfer to the fridge to chill for at least three hours.
Cut the fudge into pieces using a sharp knife.
Notes
***Instead of melting the chocolate in a double boiler, you can melt it in the microwave. Heat in 30 second intervals, stirring between intervals until the chocolate is melted.