In the bowl of a double boiler, melt the bittersweet chocolate over simmering water, stirring until completely melted. Set aside.
Rinse the sticky rice and drain.
In a large sauce pan, stir the sticky rice and water and bring to a boil over medium heat.
Lower the heat to a simmer and cook, stirring occasionally, until the rice has thickened, about 15 minutes.
Add the melted chocolate, cocoa powder and sugar, stirring well. Cook until the rice is a creamy consistency.
Serve warm with a drizzle of evaporated milk or for pure decadence, condensed milk. Regular milk can also be used.
