Butter and or line the base and sides of a 23cm round, deep cake tinCut the orange into slices, remove the pips then place everything else in a food processorWhizz the orange until you have a finely chopped pureeAdd all the remaining ingredients (except the icing sugar) and whizz together until smoothPour into the prepared tin and smooth the topBake in a pre-heated oven at 190 degrees C/170 degree fan/gas mark 5 for around 25-30 minutes until risen and firm