In a medium-sized saucepan, combine water, cocoa, sugar, corn syrup, vanilla, and salt. Place over high heat and whisk until smooth and the mixture is boiling. Remove from heat.

Add chocolate and stir until smooth.

Cover and refrigerate at least 8 hours, preferably overnight.

Churn in an ice cream maker according to the manufacturer's directions.

Pack in an airtight container and keep frozen.