Rehydrate dried mushrooms in hot water.
Sauté chopped onion in butter until softened.
Add flour to the onions and butter to create a roux, cook for a minute.
Gradually whisk in broth, ensuring no lumps form.
Add diced potatoes and rehydrated mushrooms (strained, reserving liquid).
Bring to a boil, then simmer until potatoes are tender.
Stir in sour cream, vinegar, and chopped dill.
Season with salt and black pepper to taste.
Poach eggs separately or gently in the soup.
Serve hot, garnished with extra dill if desired.
