Cut the leeks and wash them well. Also chop the celery in pieces.
Take a large souppot and melt the butter. Briefly bake the leeks and the celery in the butter. Add the thyme. Pour in the stock and cook for about 15-20 minutes or until cooked. You can puree the soup as I have done or serve it as is. Season with salt and pepper to your liking
Cut the mushrooms in smaller pieces and bake these with the bacon cubes separately in a frying pan and serve on top of the soup.