Start the Broth: In a large cooking pot such as a Dutch oven, combine 12 cups of water with the bone-in beef shanks. Add into the mix 4 garlic cloves, a couple of bay leaves, and a tablespoon of kosher salt. Heat until it reaches a boil, then cover, reduce the heat to maintain a gentle simmer, and let it cook for about 1 ½ to 2 hours, or until you find the beef nicely tender.
Clean the Broth: Throughout the cooking process, keep an eye out for any foam forming on the top and skim it off. Once the beef is tender, remove the bay leaves and garlic, discarding them. Take the beef shank out of the pot and set it aside to cool down a bit.
Introduce the Vegetables: Into the pot, add the sliced carrots, the corn halves, potato pieces, chunks of zucchini, cabbage chunks, a generous handful of cilantro, and a spoonful of tomato paste. Mix everything well to ensure the tomato paste is completely integrated into the broth.
Simmer the Vegetables: Bring the soup back up to a boil, then lower the heat to let it simmer gently. This is to ensure the vegetables become perfectly tender, which should take around 15-20 minutes.
Prepare the Beef: While the veggies are simmering away, deal with the beef shank by removing any bones and tough parts, then chopping the meat into small, bite-sized pieces. Once the veggies are tender, add the meat back into the pot.
Season and Serve: Give the soup a good stir to mix everything together, then do a taste test and adjust the seasoning with more salt if it's needed.
Enjoy Your Meal: Serve the Caldo de Res hot, garnished with additional fresh cilantro, a squeeze of lime juice from the halved limes, and a dash of hot sauce for those who enjoy a bit of heat.