Heat the mixture over medium heat, stirring constantly until it thickens and forms a smooth custard that coats the back of a spoon (about 10 to 15 minutes).
When the custard is ready, take the pot off the heat.
Pour custard over the chocolate.
Let the chocolate and custard mixture sit undisturbed for 5 minutes.
Add the Maca and vanilla and gently stir the ingredients. Steady, slow stirring is essential for ensuring a stable emulsion.
Divide the mixture evenly into espresso cups or ramekins and put into the fridge until set.