Heat sesame oil in a small saucepan over medium-low heat until warm and fragrant.
Add minced garlic and ginger, cooking for 30 seconds until aromatic but not browned.
Pour in soy sauce, brown sugar, hoisin sauce, and rice vinegar. Stir well to combine.
Bring mixture to a gentle simmer while whisking to prevent sugar from sticking.
Reduce heat and simmer for 8–10 minutes until slightly thick and glossy.
Stir occasionally and watch for slow bubbling and syrup-like consistency.
Remove from heat once it coats the back of a spoon lightly.
Let it cool for a few minutes so it thickens naturally before using.
