In a small bowl, whisk the cornstarch with a few tablespoons of milk until smooth. This helps prevent lumps later.

In a saucepan, warm the remaining milk over medium heat until it starts to steam. Add the chopped chocolate and stir until it melts completely.

Slowly pour in the cornstarch mixture, whisking constantly. Continue to cook for 3–5 minutes until the pudding thickens and coats the back of a spoon.

Pour into small bowls or glasses, cover, and refrigerate for at least an hour. Serve plain or topped with whipped cream or shaved chocolate.