Chinese Oxtail Soup

The ultimate comforting oxtail soup features beef that falls off the bone, rich tomato broth, and tender cabbage & potato. 

• 2 kg (4 to 5 lbs) oxtail , separated at joints
• 8 cups beef stock (or water) 
• 2 tablespoons olive oil
• 1 big onion , coarsely chopped
• 4 carrots , chopped
• 1 thumb ginger , sliced
• 4 Yukon gold potatoes , chopped
• 28 oz (800 g) tomato , diced
• 2 tablespoons tomato paste
• 3 bay leaves
• 1/4 head cabbage , chopped
• 2 teaspoons sugar
• 1 teaspoon coarse sea salt
• 1/2 teaspoon coarse black pepper
• Heavy cream sour cream, or plain Greek yogurt for garnish