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 9-inch springform pan and bake in a preheated 44 F oven for 30 minutes, then reduce the temperature to 325 F 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.