Please understand that this is not a traditional beverage in Ghana. Ghana's world-class cocoa, and its cassava consumption, inspired me. I'm not sure how it will work with powdered or evaporated milk but I'll continue experimenting, including a stove-top version, different kinds of milk, using coconut milk/water, different types of chocolate, flavorings like vanilla, mint, etc. Also, I wonder about how to extract the cassava (tapioca) starch directly from fresh cassava. . .
I took a mug of milk (probably 12-14 oz, half whole milk and half organic 1%) and whisked in 2 teaspoons of tapioca starch (aka tapioca flour). I heated it for a few minutes, stirring every 30 seconds or so (not sure if this is necessary, but I didn't want it to thicken unevenly). After a couple of minutes, I added some squares of chocolate I had handy (Lindt's 85% extra dark cocoa, probably 3/4 - 1 oz; the Lotte "Ghana" chocolate my Berkeley daughter gave me from her trip to Japan was too precious to experiment with), whisked it with a tiny whisk as it melted, and put it back in the microwave for about 30 seconds, then whisked it again. It needed a little sugar . For garnish I used grated chocolate and a little whipped cream.
It was luxuriously rich, smooth, creamy, and very satisfying. I invite you to try it and let me know what you think (and also how to improve it).