Combine cocoa, sugar, and salt in a saucepan. Add water, and mix until smooth.
Bring this mixture to a boil. Allow it to boil for one minute, be careful this does not over boil.
Remove from heat, when this cools add the vanilla.
Recipe Tips
The secret to achieving that distinctive Hershey's flavor is using their specific cocoa powder, which has a slightly more acidic profile than other brands. This creates that subtle tanginess that makes Hershey's chocolate instantly recognizable. For the smoothest texture, make sure to whisk continuously during the initial mixing phase—any undissolved cocoa will create lumps that are difficult to remove later. If gifting this syrup, consider adding a decorative label that notes the two-week refrigerated shelf life.