In a medium saucepan, combine the water and sugar. Heat over medium heat, stirring until the sugar is completely dissolved.
Whisk in the cocoa powder, vanilla extract, and salt until smooth and well combined. If using corn syrup, add it now and stir until fully incorporated.
Remove the saucepan from heat and let the mixture cool to room temperature.
Once cooled, transfer the mixture to a shallow dish or a bowl and place it in the freezer.
After 1 hour, remove the dish from the freezer and stir the mixture with a fork to break up any ice crystals. Return to the freezer.
Repeat the stirring process every 30 minutes for about 2-3 hours, or until the sorbet is firm and has a smooth texture.
Once ready, scoop the sorbet into bowls and serve immediately or store in an airtight container in the freezer for later.