In a large bowl, beat the ricotta cheese, heavy cream, rum, chocolate flavoring, cocoa and sugar until very smooth and creamy. Pour the mixutre into a well-buttered 23 cm springform pan and bake in a preheated 10ºC oven for 30 minutes, then reduce the temperature to 160ºC and continue to bake for another hour, or until golden brown.
Transfer to a wire rack and allow to cool completely.
When completely cooled, remove the sides of the springform pan and decorate the top of the cake with the confectioner's sugar.
Either refirgerate or serve immediately.