Heat the cream in a saucepan over medium-low heat until it begins to bubble. Remove from the heat and stir in the chocolate and sugar until melted. Slowly stir in the Guinness®. Cover and refrigerate until completely cooled.
Pour the chilled mixture into an ice cream maker and freeze according to manufacturer's directions until it reaches a soft consistency. Transfer ice cream to a two-litre lidded plastic container; cover surface with cling film and seal. For best results, ice cream should ripen in the freezer for at least 2 hours or overnight.