Start by gathering and preparing all the soup ingredients. Bring 4 cups of water to a boil.
Add the dried wild mushrooms to the boiling water, cover, and let them soak for 30 minutes. (Skip this step if using fresh mushrooms.)
At this point, the mushrooms should be fully hydrated.
Use a strainer to remove and drain the mushrooms, but be sure to save the soaking liquid.
This reserved mushroom liquid will be used later for the soup base.
Cut the rehydrated (or fresh) mushrooms into ½-inch cubes.
Preheat a Dutch oven over medium heat.
Pour the oil into the pot and let it heat for 1 minute.
Add the chopped onion and sauté, stirring regularly.
Stir in the minced garlic, cubed mushrooms, and sliced carrots.
Let everything cook uncovered over medium heat for 7–10 minutes, stirring occasionally.
Add the sour cream and flour, mixing until smooth and well combined.
At this stage, the soup should be thick and flavorful.
Pour in the chicken broth, reserved mushroom liquid, bay leaves, dill, black pepper, and diced potatoes. Cover and cook over medium heat for 20 minutes.
Add the rinsed barley, reduce the heat to low, and cook for another 12 minutes.
Remove the bay leaves. Finally, serve the creamy mushroom soup garnished with fresh sprouts, green onions, croutons, dill, sourdough bread—or your favorite toppings.