In a saucepan, whisk together heavy cream, cocoa powder, sugar, and salt until fully combined

Heat the mixture over medium heat until it begins to steam, stirring continuously

Remove from heat and add chopped dark chocolate, stirring until melted and smooth

Add whole milk and vanilla extract, mixing thoroughly

Allow the mixture to cool to room temperature, then refrigerate for at least 2 hours

Pour the chilled mixture into an ice cream maker and churn until thick and creamy

Transfer to an airtight container and freeze for 3–4 hours until firm

Let sit at room temperature for a few minutes before scooping