Slice mushroom thinly.
Melt the butter in a heavy-based pan and saute the onion, garlic and thyme for 1 minute.
Add flour and keep stirring for a minute.
Throw in the mushroom and season with salt and black pepper. Cook until the mushroom just softens.
Pour in broth and stir continuously.
Reduce the heat and simmer gently for a few minutes, stirring occasionally.
Pour in milk and once it almost reaches a soft boil, add in cream into the soup.
Reheat gently, stirring. Do not allow the soup to boil. Season with more salt and pepper, and garnish with some chopped parsley/thyme.