Prep. Remove the stems from the blueberries. Remove the seeds from the jalapeno pepper and mince the pepper. Mince the onion.
Cook. Heat the oil over medium heat in a medium saucepan or cast iron skillet. Add the minced onion and jalapeños and cook until they are softened, about 4 minutes, stirring a few times. Stir in the blueberries, brown sugar, vinegar, ketchup, mustard, and Chipotle Tabasco sauce. Bring to a boil, then reduce the heat to medium-low and simmer for 15 minutes, stirring often.
Puree. Use an immersion blender or upright blender to puree the sauce until smooth. If you used an upright blender, return the mixture to the saucepan and stir in the butter until melted. Season to taste with salt, if using.
Serve. Use immediately, or cool and store in an airtight container in the refrigerator for up to 1 week.