In a Dutch oven, cook onion, garlic, ½ cup tomato sauce and olive oil until onion is tender. Add broth and ½ cup tomato sauce; bring to a simmer.
Meanwhile, in a large bowl, mix ground beef, rice, egg, salt, pepper, milk, cumin, saffron, crushed crackers and remaining ½ cup tomato sauce until combined. With wet hands, form into 1-in. balls. Gently add meatballs to simmering broth; cook, stirring occasionally, 20-25 minutes. Serve with tostadas and cabbage if desired. Garnish with cilantro.