Let a large skillet get heated over medium heat; add in the oil; then add in the onion, carrot, celery, and garlic; stir/saute 5-7 minutes or until softened.

Stir in the tomato paste, tomato puree, vinegar, molasses, and Worcestershire sauce; bring to a simmer.

Lower heat to low and let simmer gently for 45-60 minutes or until thickened and the flavors have melded.

Add in a little water if the sauce gets too thick or dry.

In another large skillet over med-high heat, brown the ground beef, breaking the meat apart into small pieces; cook until the meat is no longer pink; drain.

Add the sauce to the meat and simmer over med-low for at least 10 minutes or until the flavors blend.

Serve by spooning ½ cup of the filling over half a toasted hamburger bun and topping with the other half.