- In a saucepan, combine half the sugar with the cocoa powder and cornstarch. Add the milk and corn syrup and bring to a boil, stirring with a whisk. Set aside.
- In a bowl, combine the remaining sugar with the egg yolks. Add the hot milk mixture while stirring. Add the chocolate and let rest for about 1 minute. Stir to combine until smooth.
- Cover and refrigerate for about 2 hours or place the bowl over an ice bath to cool the mixture faster.
- Churn the milk mixture into an ice cream maker according to the manufacturer's instructions until the mixture has frozen. Transfer to an airtight container and freeze. Let rest at room temperature for a few minutes before serving.