This is based on about 250gm or 8oz mushrooms. It's hard to be precise on the quantity, because I usually make soup when the mushrooms have been left in the fridge or pantry too long and have dried out, so they weigh less than when bought. If they aren't dried out, they become a breakfast omelette instead
. I make soup with leftovers as I don't like waste.
For soup I don't bother peeling the mushrooms. If the mushrooms are very dry, soak them in enough chicken stock to cover them for a while until they are soft again; if not don't bother. Strain the liquid off and retain it.
Fry a medium/large sliced onion in a couple of tablespoons of olive oil and a nob of butter until just starting to caramelise. Sometimes I add a clove of garlic, but not always. Chop the mushrooms roughly and add to the onions, frying gently. Cook briefly, then add about a litre/quart of chicken stock (including any reserved liquid) and bring to a simmer. Season with salt (mushrooms need a little extra salt), grated black pepper and the secret ingredient: some grated nutmeg to taste. Simmer for about half an hour; longer if the mushrooms were originally very dry. I like some texture; before I use the stick blender I strain out about a half cup of the mushrooms and reserve them.
Then I blend the soup, not quite to puree, and return the lumpy bits. If the result is too thick, add more stock and cook it in for a little while. If it is too thin, simmer a bit longer to reduce it. When serving add a large dollop of real cream in the centre of the soup in each bowl.
The only significant carb content is the onion. That allows me to have a slice of buttered bread with it