Heat 2 tablespoons of olive oil in a large stockpot over medium-high heat. Cut the roast beef into 2-3 inch chunks and season with kosher salt and black pepper. Brown the beef in batches for about 3-4 minutes each and set aside.

In the same pot, add 3 tablespoons of tomato paste and stir for about 1 minute. Pour in 5-6 cups of beef broth and water, deglazing the pan. Return the beef, reduce heat to medium, and simmer for 1.5 to 2.5 hours until fork-tender.

Chop 2 cups of leeks, 1 cup of celery, and 3 cups of carrots into bite-sized pieces. Mince 4 cloves of garlic and set all the vegetables aside.

Heat an additional tablespoon of olive oil in the same pot over medium heat. Add leeks, celery, carrots, 1 teaspoon of thyme, and a pinch of salt and pepper. Sauté for about 4-5 minutes, then add minced garlic and cook for an extra 30 seconds.

Stir in the 15-ounce can of tomato sauce, the reserved beef broth, and 10 cups of chopped cabbage. Add 1 tablespoon of Worcestershire sauce and 3 bay leaves. Bring to a boil, then reduce the heat to a gentle simmer for about 10-15 minutes until cabbage is tender.

Ladle the soup into warm bowls and enjoy with crusty bread or crackers for a satisfying meal.