01 - In a medium saucepan, whisk together the cocoa powder, sugar, and salt.
02 - Add the water and whisk until the mixture is smooth.
03 - Place the saucepan over medium heat and bring to a gentle boil, stirring constantly.
04 - Reduce heat and simmer for 2 to 3 minutes, stirring frequently until the syrup thickens slightly.
05 - Remove from heat and stir in the vanilla extract.
06 - Let the syrup cool slightly; it will thicken further as it cools. Transfer into a clean jar or squeeze bottle and refrigerate for up to two weeks.