How to cook
If the porcini mushrooms are dried soak the in warm water for around 20 minutes and strain them.
Clean and slice the button mushrooms, the size of the slices is not of great importance.
Heat the olive oil and butter in a large heavy bottom pan. Add the mushrooms and saute them, until the released juices evaporate. Transfer the mushrooms into a bowl, pour in the milk and blend them to a smooth texture. Set aside.
Bring the water to a boil in a pot, add the vegetable stock, or stock cubes, and the potato, chopped into large chunks.
Cook on moderate heat for 6-8 minutes, until the potatoes are soft but not overcooked.
Add the mushrooms and cream, blend and season with salt. If needed you can add the cornstarch dissolved in a little cold water. Cook for 3-4 minutes.
Remove from the stove and season with freshly ground black pepper.