To a medium-size pot, add butter and onion. Sautee over medium-high heat until translucent. Whisk in tomato paste and vinegar and cook for 1 minute.
Add Dr. Pepper, ketchup, brown sugar, honey, Worcestershire sauce, chili powder, garlic, and salt. Stir together. Bring the sauce up to a boil then reduce to simmer for approximately 10 minutes until thickened.
Remove sauce from the stovetop and let cool. Using an immersion blender or a stand blender, process sauce until smooth.
Serve immediately or store in the refrigerator for up to 3 months.