To make the poached rhubarb, preheat the oven to 170C (not fan-forced).
Place rhubarb in a baking dish with the sugar and orange juice. Cover and bake in the oven for 20 minutes or until soft, then set aside to cool.
Increase the oven to 180C. Grease a 23cm springform cake pan.
Place the butter and marzipan in a food processor with the coconut cream and sugar. Process until combined and smooth. Add the coconut essence, then break the eggs down the funnel of the processor, one at a time, with the motor running. Lastly, add the flour, and desiccated coconut and process again, stoping once or twice to scrape down the sides so that you have a smooth cake batter. Pour the batter carefully into the prepared cake pan and baked for 1 hour, or until a skewer inserting into the centre comes out clean. Cover the cake with foil for the last 15 minutes of cooking if it is browning too quickly.
Remove the cake from the oven and allow to cool slightly in the pan before turning onto a wire rack. When you are ready to serve, dust the top of the cake with icing sugar, scatter with toasted flaked coconut, and top with poached rhubarb. This cake is best served slightly warm.