Heat 1 cup (250ml) cream over low heat in a saucepan. Add the diced chocolate and stir constantly until melted.
In another saucepan, combine 4 tablespoons water with the sugar. Bring to a boil and simmer 3 minutes until syrupy. Let cool slightly.
With an electric mixer, beat the egg yolks and salt until fluffy, about 1 minute. Pour in the syrup in a thin stream while beating on medium speed.
In a large bowl combine the egg mixture with the chocolate mixture, then add vanilla and remaining cream, beating until smooth. Place in the fridge for 1 hour, then transfer to the ice cream maker and churn as per manufacturer's instructions.