Bake the churros according to the package instructions, or reheat them in an air fryer until warm and crispy.
Pour the milk into a saucepan with the chocolate. Cook on a low heat, stirring continuously, until the chocolate has melted. Add the cornstarch to a 1/2 tablespoon of water and add it to the chocolate mixture. Whisk well. Add the sugar. Cook for 5 minutes, whisking, until the mixture has thickened.
Serve the churros with the chocolate, however you like.