Whisk together the cream, cocoa powder, and sugar in a large saucepan. Heat the mixture, whisking frequently, until it comes to a full, rolling boil (it will start to foam up). Remove from the heat and add the raspberries. Cover and let stand for 10 minutes.
Purée the mixture in a food processor or blender. If you wish, press the mixture through a mesh strainer to remove the seeds. Chill the mixture thoroughly, then freeze it in your ice cream maker according to the manufacturer’s instructions.
Adapted from the Perfect Scoop