While rice is cooking, beat the egg in a bowl. Add the milk and stir well to mix. Add the egg mixture, vanilla extract, condensed milk and orange rind to the rice and cook over low heat, stirring carefully, until most of the liquid evaporates and the rice reaches the desired consistency, about 30 minutes. Add the sweet potato puree and, stir until heated thoroughly remove from heat. Serve, top with a spoonful of marshmallow cream and sprinkle orange rind to decorate.