In a Dutch oven, over medium heat, bring the beans, broth, garlic, bay leaf, and carrots to a boil. Cover, reduce heat, and simmer for 15 minutes. Remove and discard the bay leaf. Add the spinach, salt, and pepper and stir for 1 minute. Spoon the stew into bowls. Drizzle with the oil. If desired, add either some vinegar or Parmesan.