In the pre-heated pressure cooker on medium-high heat, add the olive oil and saute' the thinly sliced mushrooms on both sides until golden (about 5 minutes). Remove the mushrooms and set aside.

Now, add the celery and onions and saute' them until the onion has softened.

Push the vegetables to the side and add enough roughly-sliced mushrooms to cover the base of the pressure cooker (probably two handfuls) and brown them lightly by stirring infrequently (about 5 minutes).

Pour in the wine and use the wine's liquid to lift the brown bits from the base of the booker to incorporate them into the recipe and evaporate the wine completely.

Add the remainder of fresh mushrooms (not the sliced and sauteed mushrooms), dried mushrooms, potatoes, vegetable stock, and salt (if using) and mix well.

Close and lock the lid of the pressure cooker. For stove top pressure cookers, turn the heat up to high and when the cooker reaches pressure, lower to the heat to the minimum required by the cooker to maintain pressure. Cook for 5 to 7 minutes at high pressure.

When time is up, open the cooker by releasing the pressure.

Add the fresh cream, pepper and truffle spread (if using) and, using an immersion blender, puree the contents of the pressure cooker.

Stir in the sliced mushrooms (reserving a few for garnish) and serve.