Mix the sugar, starch, cocoa and salt in a saucepan. Whisk the milk and egg yolk and pour in with a whisk while stirring, stirring well so that no lumps form. Cook for about 1-2 minutes, stirring over medium heat, until the mixture has a thick creamy consistency. Add the chocolate to the cream together with the butter. Stir until both are melted.
Pour the cream into small cups and chill for about 2 hours.
Before serving, whip the cream, vanilla sugar and cardamom until stiff. Serve the chocolate cream with a dollop of cardamom cream and dust a touch of cardamom over the cream.