If you’re using dried porcini, soak them first in hot water or broth for about 15 minutes until soft. Once rehydrated, drain them and continue with the recipe as written.
Clean the fresh porcini gently with a brush or damp cloth and slice them into larger pieces — they’ll shrink as they cook. Prepare the rest of the vegetables: peel and dice the potatoes into small cubes, slice the carrots thin, finely chop the onion, and crush the garlic.
Warm a mix of olive oil and butter in a large pot. Add the onion and garlic and let them cook slowly until soft, fragrant, and golden. This forms the flavor base of your soup.
Stir in the carrots and cook for a minute or two so they release their sweetness, then add the porcini. Keep stirring while they fry gently (you want them to caramelize just a little).
Add the potatoes and pour in enough vegetable broth (or water) to fully cover the ingredients.
Once the soup comes to a boil, lower the heat, cover with a lid, and let it simmer slowly for about 30 minutes.
When the potatoes and carrots are tender, pour in the white wine and let everything simmer for another five minutes.
Take out a few spoonfuls of potatoes, mash them with a fork, and stir them back in. This will thicken the soup naturally without needing flour or starch.
Stir in the sour cream (or cooking cream, if you prefer a milder taste). At this stage, you can blend the soup with a hand blender for a smooth texture or leave it rustic with visible chunks.
Finish with a handful of fresh parsley and give it another minute to mingle with the flavors. Serve the soup hot with garlic croutons or homemade bread.