Wash and chop the mushrooms, coriander and spring onions. Bring the water to the boil and mix with the stock cube in a measuring cup.
Heat the finely chopped mushrooms in a pan without oil. As soon as the mushrooms lose their size and water, add olive oil. Then add the finely chopped spring onions and the finely chopped red onion. Pour in the vegetable stock and set the stove to medium heat. Add the soy sauce and crème fraîche and stir. Possibly season with salt.
Finally, sift a little flour over the sauce and thicken. Add the finely chopped coriander and season with a little nutmeg.