Preheat oven 120°C fan forced. Trace a 20cm x 30cm rectangle on a piece of baking paper. Place baking paper, trace-side down, on a large, greased baking tray.
Place the egg whites in the bowl of an electric mixer, whisk on high speed until soft peaks form. Add the caster sugar, one spoon at a time, beating until the sugar has dissolved. Once all the sugar has been added, scrape down the side of the bowl and continue whisking on high speed for 5 minutes or until the meringue is thick and glossy. Combine the cornflour and vinegar in a small bowl, stir until smooth then add to the meringue, whisk for 15 seconds.
Drop large spoonful’s of the meringue into the rectangle shape, using the pencil mark as a guide. Bake for 1- 1½ hours, or until pavlova feels dry and crisp. Turn oven off, leave the door ajar and allow the pavlova to cool completely in the oven. Using the baking paper, lift the pavlova onto a serving plate or board.
For the cannoli cream; beat the ricotta, vanilla and sugar with an electric mixer until well combined and creamy. Stir in the custard, chocolate and pistachios. Spoon the mixture evenly over the pavlova.
Cut the mango cheeks from the stones. Using a large spoon, remove the mango fruit from the cheeks and thickly slice the fruit. Arrange the mango over the cannoli cream. Serve.
TipOn a hot summers day, make the pavlova on the morning of serving. The cannoli cream can be made up to 6 hours ahead. Decorate the pavlova just before serving.