Add the water and sugar to a small pot and bring to a boil.

Turn the heat down to low and add the cocoa powder. Whisk until all of the solids have dissolved.

Add the vanilla, salt and corn syrup. Stir well.

Reduce the sauce until slightly thickened. Don't worry if the sauce is a bit runny as it will thicken up when cooled.

Strain the sauce to remove any solids that remain.

Pour the sauce into a jar and cool to room temperature.

Use immediately or store in the refrigerator in an airtight container.