Season the brisket liberally with salt and pepper.
Heat the oil in a large dutch oven over medium/high heat. Add the brisket to the pot and brown on all sides, working in batches if necessary. Do not crowd the pan.
Using a slotted spoon, transfer the browned beef to a platter or plate.
Add the onion, celery and carrot to the pot. Cook for 2-3 minutes or until beginning to soften. Stir in the tomato paste and italian seasoning. Cook for 1 minute.
Stir in the cabbage and beef stock. Bring the soup to a boil.
Add the worcestershire sauce, vinegar, brown sugar and bay leaf. Stir to combine. Return the beef to the pot and cover.
Turn the heat to low and simmer, covered, for 30-45 minutes.
Season with salt and pepper, to taste. Serve immediately