Heat a frying pan with vegetable oil and fry the onion until golden brown, then add the mushrooms and simmer until done.
Puree the mixture until smooth.
Melt the butter in a saucepan, add the flour and stir well. Pour in some of the broth and stir again.
Add chopped mushrooms and onions, pour in the remaining broth and bring to a boil.
Pour in the cream, add salt, pepper and stir well so that the spices are evenly distributed in the soup.