Cut the leeks and wash them well. Also chop the celery in pieces.
Take a large souppot and melt the butter. Start by baking the onions until translucent. Add the garlic and the rest of the vegetables. Briefly bake them too. 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.