Slow-Cooker Cabbage Soup with Sherry

Heat oil in a large skillet over medium-high heat. Add carrots, leek, celery and garlic; cook, stirring often, until tender, about 5 minutes. Add thyme; cook, stirring often, until fragrant, about 1 minute. Add sherry; bring to a boil. Boil, undisturbed, until reduced by half, 1 to 2 minutes. Remove from heat; transfer the mixture to a 6-quart slow cooker.

Add broth and tomatoes to the slow cooker; stir well to combine. Stir in cabbage, potatoes, barley, salt and crushed red pepper. Cover and cook on High until the cabbage is tender and the potatoes are cooked through, about 4 hours. Stir in sherry vinegar.

Divide the soup evenly among 6 bowls; garnish with parsley, if desired. Serve immediately.