1 cup Great Northern beans
6 cups water
1 (14-ounce) can whole tomatoes
3 cloves garlic, crushed
2 ribs celery, chopped
2 medium carrots, chopped
1 small onion, chopped
1/2 cup pearl barley
1 bay leaf
2 tablespoons kosher salt, or more to taste
2 teaspoons dried Italian seasoning
Freshly ground black pepper
1/2 ounce dried porcini mushrooms
3 cups baby spinach leaves, checked (about 3 ounces)
1 tablespoon balsamic vinegar
Put beans, water, canned tomatoes, garlic, celery, carrots, onion, barley, bay leaf, 1 1/2 tablespoons salt, Italian seasoning, pepper, and porcini mushrooms in a slow cooker; cover and cook on low until the beans are quite tender and the soup is thick, about 8 hours.
Stir in the spinach, and vinegar, cover, and let the soup cook until the spinach wilts, about 5 minutes. Taste and season with salt and black pepper, to taste.
Serve with crusty bread for a satisfying warm meal!