Polish Mushroom Soup (Zupa Grzybowa)

Soak the dried wild mushrooms in warm water for about 30 minutes until softened. Drain and reserve the soaking liquid, straining it to remove any grit.
Slice the fresh mushrooms and set them aside.
Sauté the Vegetables:

In a large pot, melt the butter over medium heat. Add the finely chopped onion, carrot, and celery. Sauté for about 5-7 minutes, or until the vegetables are softened and the onion is translucent.
Cook the Mushrooms:

Add the sliced fresh mushrooms to the pot and cook for another 5 minutes, allowing them to release their moisture and become tender.
Chop the soaked dried mushrooms into smaller pieces and add them to the pot, along with the reserved soaking liquid (be careful not to pour in any sediment). Stir to combine.
Add Broth and Seasonings:

Pour in the vegetable or chicken broth and bring to a boil. Add the dried thyme, bay leaf, salt, and pepper. Reduce the heat and simmer the soup for about 25-30 minutes, allowing the flavors to meld together.
Thicken the Soup:

In a small bowl, whisk together the flour and a bit of cold water to create a smooth slurry. Gradually stir the slurry into the soup to thicken it, cooking for another 5 minutes.
Add Sour Cream (Optional):

For a creamier version, stir in the sour cream at the end of cooking. Adjust the seasoning with salt and pepper to taste.
Serve:

Remove the bay leaf and serve the soup hot. Garnish with fresh parsley, if desired.
Serving and Storage Tips: