Chop the chocolate and put it in a bowl.
Bring the cream and the milk to a boil in a pot. When it’s boiling, pour some in the egg yolk/sugar, whisk and transfer back into the pot. Cook like a creme anglaise – 83°C – on a low to medium heat and stir until it thicken and the foam is gone.
Pour half of the custard on the chocolate, mix well, and add the rest of the custard.
Pour the chocolate custard in two ramekins and refrigerate for at least 3 hours.