Stir together all ingredients in a small saucepan. Bring to a rapid simmer over medium-high heat.
Reduce to a gentle simmer over medium-low heat. Simmer uncovered for 4-5 minutes, scraping down the saucepan sides with a spatula as needed. The BBQ sauce is ready when the sugar is melted and the sauce has thickened to desired consistency. Taste for salt and spice. Note that the sauce will thicken as it cools.
Tomato sauce: Choose an unflavored sauce. You can use an equal amount of ketchup in place of tomato sauce but it will yield a thicker and sweeter sauce.
Mustard: I love using stone ground mustard for extra depth. You can use ground mustard or spicy brown mustard but it will alter the flavor slightly.
Leftovers: For best quality keep refrigerated in a closed container for 4-5 days.
Freezing: Transfer cooled sauce to a room temp container. I like using Ball jars. Make sure to leave at least ½ inch at the top. Cover and freeze for up to 3 months. Let thaw overnight in the fridge when ready to use.