In a medium saucepan, combine the plums, garlic, onion, chipotle pepper, ketchup, tomato paste, brown sugar, apple cider vinegar, Worcestershire sauce, smoked paprika, salt, and black pepper.
Pour in the water and mix everything together.
Bring the mixture to a boil over medium heat.
Reduce the heat to low and let it simmer for 20-25 minutes, stirring occasionally.
Remove the sauce from the heat and let it cool for a few minutes.
Pour the sauce into a blender or food processor and blend until smooth.
Using a fine mesh strainer, strain the sauce to remove any chunks or seeds.
Pour the sauce back into the saucepan and bring it to a simmer over low heat for a few minutes to thicken.
Remove from heat and let it cool.
Pour the barbecue sauce into a mason jar or airtight container and store in the fridge until ready to use.