Add all ingredients to a medium saucepan and whisk until smooth.
Bring the mixture to a gentle simmer over medium-low heat.
Reduce heat to low and simmer for 12–15 minutes, stirring occasionally, until slightly thickened.
Remove from heat and cool slightly before using. The sauce will continue to thicken as it cools.
Notes
Whisk everything together at the start to break apart any lumps in the brown sugar. The lumps won't dissolve as easily once the sauce starts heating.
Simmer gently over low heat to prevent burning. The sugar content makes this sauce prone to scorching if the heat is too high.
Stir occasionally while simmering to prevent sticking on the bottom of the pan. A quick stir every few minutes does the trick.
Pull the sauce off the heat when it's slightly thinner than you like. It will continue thickening as it cools and will thicken even more when refrigerated.
Dark brown sugar adds deeper molasses flavor while light brown sugar keeps the sauce brighter. Either works perfectly so use what you have.
Taste and adjust before it cools completely. It's easier to add more vinegar for tang or brown sugar for sweetness while the sauce is still warm.
Make it your own by adjusting the spice level, sweetness, or tang to match your preferences. Start with the recipe as written, then tweak it to your taste.
Store it in a squeeze bottle for easy drizzling and less mess when grilling or serving.