Warmth butter and oil in massive skillet over MED/MED-HIGH warmth. Add beef and brown, breaking up into crumbles because it cooks, about 5 minutes. Drain.
Add onion and bell pepper to identical skillet and cook dinner 2-3 minutes, till mushy. Add garlic and cook dinner 30 seconds or so, till aromatic. Add beef again to the skillet and add tomato paste. Stir effectively.
Add ketchup, water, brown sugar, mustard, chili powder, Worcestershire sauce, salt, purple pepper flakes (if utilizing), and black pepper. Stir effectively to mix.
Cook dinner over MED warmth for 10-Quarter-hour, till combination has thickened to your liking. Take away from warmth and serve over toasted buns