In a small saucepan set over low-medium heat, add water, sugar, cocoa powder, salt, vanilla extract, and espresso powder. Whisk to combine so that all ingredients dissolve and are smooth. Allow mixture to come to a simmer, whisking frequently.
Once mixture begins to simmer, add Kahlua (or preferred coffee liqueur) and continue to simmer and thicken for 2-4 minutes, still whisking frequently.
Once mocha syrup is to your preferred thickness, remove from heat and pour into a heat-safe container to cool to room temperature. Store syrup in the refrigerator.
Nutritional information is provided as an estimate. As it can vary due to many factors (brands used, quantities, etc.), we cannot guarantee its accuracy.