Slow-Cooker Bean and Barley Soup

INGREDIENTS

• 1/2 cup pearl barley
• 3 cloves garlic, smashed
• Special Equipment: slow cooker
• 1/2 ounce dried porcini mushrooms, crumbled if large, optional
• 1 bay leaf
• 3 cups cleaned baby spinach leaves (about 3 ounces)
• 2 teaspoons dried Italian herb blend
• Freshly ground black pepper
• Kosher salt
• 1/2 medium onion, roughly chopped
• 2 medium carrots, roughly chopped
• Extra-virgin olive oil, for drizzling
• One 14-ounce can whole tomatoes, with juice
• 1 cup dried multi-bean mix or Great Northern beans, picked over and rinsed
• 2 ribs celery, roughly chopped
• 1/4 cup freshly grated Parmesan Balsamic vinegar, for drizzling