In a suitable saucepan, combine the milk, starch, and chocolate. Stir well.
Cook the mixture over medium heat, stirring constantly, until it boils and thickens.
Pour the custard into a water-soaked mold and smooth the surface.
Refrigerate for at least 4 hours to set.
Once set, remove the custard from the mold and slice it.
Decorate and serve as desired.
Enjoy your delicious sliced chocolate custard! Bon appetit to those who try it in advance.