Prepare the Barley: Rinse the pearl barley under cold water, place it in a pot, cover with water, bring to a boil, cook over medium heat for 20 minutes, then drain and set aside.
Prepare the Mushrooms: If using dried mushrooms, soak them in warm water for 20-30 minutes until soft, then drain and set aside. If using fresh mushrooms, slice them and set aside.
Sauté the Vegetables and Mushrooms (If Fresh): Heat olive oil in a large skillet over medium heat, sauté chopped onion and diced carrots for 5 minutes until soft and golden, add sliced fresh mushrooms, cook for another 5-7 minutes until tender, then add minced garlic and cook for 1 minute.
Cook the Mushrooms (If Dried) and Add Sautéed Vegetables: Bring 8 cups of water to a boil in a large pot, add soaked dried mushrooms and diced potatoes, cook for 10 minutes, then add the sautéed vegetables.
Add Barley and Seasonings: Add the pre-cooked barley and bay leaf to the soup, season with salt and pepper, and simmer over low heat for 20-30 minutes until potatoes and barley are tender.
Serve: Remove the bay leaf, ladle the soup into bowls, garnish with fresh herbs, and serve hot.