To make the mocha sauce, start off by taking a medium sized saucepan and place it over a burner on medium low heat.
Into the saucepan add the sugar, cocoa powder, corn syrup, and water. Whisk all the ingredients together.
Continue heating the mixture over medium low, stirring continually until the mixture begins to simmer.
When it comes to a simmer, set a timer for two minutes, and continue whisking.
After the timer is up, remove the saucepan from your burner.
Whisk in vanilla, and lemon juice. Allow the mixture to cool.
You can add the mocha sauce to your coffee or espresso, then enjoy right away. Or, you can pour the cooled mixture into a mason jar, and cover with a lid. Store in the fridge for up to one week.