In a large deep pan, mix all the ingredients except for the sugar and, bring to a quick boil. Stir to incorporate the chocolate powder and to prevent rice from sticking to the pot. Once it has boiled, lower the heat and bring to a simmer.
Stir once in a while and cook until rice is tender. It may take up to 25-30 minutes for the sticky rice to cook.
When the mixture becomes a bit dry and the rice has not softened yet, you may pour in more milk or water, as needed, until the rice is fully cooked and the desired consistency is reached.
Add the sugar and mix it in.
Serve warm in bowls, with a drizzle of condensed milk in a swirl on top.