1Peel off any tough outer skins of the mushroom caps and throw them away, then slice the mushrooms finely. Heat a large saucepan over a medium heat and pour in a splash of olive oil.
2Add the onion, celery, garlic, parsley stalks, thyme leaves and mushrooms, place a lid on top and sweat gently until softened.
3Spoon 4 tablespoons of mushrooms out of the pan and put to one side. Pour the stock into the pan and bring to the boil. Turn the heat down and simmer for 15 minutes.
4Season with salt and pepper, then whiz with a hand-held blender until smooth. Pour in the cream, bring just back to the boil, then turn off the heat.