PREPARATION:
-Heat butter and oil in large skillet over MED/MED-HIGH heat. Add beef and brown, breaking apart into crumbles as it cooks, about 5 minutes. Drain.
-Add onion and bell pepper to same skillet and cook 2-3 minutes, until soft. Add garlic and cook 30 seconds or so, until fragrant. Add beef back to the skillet and add tomato paste. Stir well.
-Add ketchup, water, brown sugar, mustard, chili powder, Worcestershire sauce, salt, red pepper flakes (if using), and black pepper. Stir well to combine.
-Cook over MED heat for 10-15 minutes, until mixture has thickened to your liking. Remove from heat and serve over toasted buns.
