Combine all ingredients for the sauce in a medium size mixing bowl and whisk together to combine thoroughly.
Pour sauce into slow cooker or medium size sauce pan. If you’re using the slow cooker select low heat, place the lid on it, and you can pretty much let it go for an hour or two. If you’re using the sauce pan, place over very low heat and put the lid on to prevent splatters. Whisk every 10 minutes to prevent the sauce from burning for an hour.
Let sauce cool to room temperature before transferring into a glass container and storing in the refrigerator.
Notes
St. Louis style sauce differs from Kansas City style sauce, despite these cities both being in Missouri. BBQ is funny that way, from one side of a state to another, flavor profiles change. In this case, you’ll find the St. Louis style sauce to be a bit more tangy and less sweet than the Kansas City style sauce.