24-Hour Onion Soup

When onion soup is made in a slow cooker the flavor becomes intense—especially when it’s simmered for 24 hours. Make the beef stock and leave it in the slow cooker overnight; the resulting broth is rich in vitamins and minerals, including calcium, magnesium and phosphorus, which promote strong bones. It’s also good for digestion and boosting immunity. In the morning, add the remaining ingredients and let everything simmer all day on low heat. The deeply flavored soup will be ready by dinnertime.