In a large pot, cook the diced bacon over medium heat until crisp. Remove bacon with a slotted spoon and reserve ¾ cup for later. Discard all but 2 tablespoons of the bacon fat from the pot. Add the diced onion, carrots, and celery to the pot. Sauté for 5 minutes, until softened. Add the garlic and cook for 1 additional minute, stirring constantly. Stir in the chicken broth and beans. Season with salt and pepper to taste. Bring to a gentle simmer and cook for 1 hour, stirring occasionally. Remove ½ of the soup and purée until smooth, then return it to the pot. Stir in the tomato sauce and ¾ cup reserved bacon. Heat through. Taste and adjust seasoning if needed. Serve hot.