In a medium saucepan set over medium heat, bring the water, sugar, and salt to a boil. Remove the pan from the heat. Scrape the seeds of the vanilla bean into the pan, toss in the pod, and add the chocolate husks (if using). Steep for 10 minutes. Put the cocoa powder in a large bowl. Strain the steeped liquid through a fine-mesh strainer into the cocoa and whisk until smooth. Return the mixture to the saucepan and bring to a boil over medium heat. Reduce to a simmer and cook for 2 minutes, stirring constantly. Strain the mixture again, and then let cool. Store in an airtight container in the refrigerator for up to 14 days.