It is a cinch to pull together during naptime, or anytime, and it freezes well if you make a big batch. This is also one of the soups we've been using to introduce our daughter to mushrooms. She was initially skeptical but is now embracing it much more. For added flavor I suggested using shallots or onions, or even adding a pinch of red pepper! ---
1. Trim the leeks and use only the white and green parts. Cut them into thin rounds, no more than ½-inch thick. Plunge the rounds into a bowl of cold water and swish them around thoroughly to wash any dirt out of the leeks. Repeat this until the water is completely clean.
2. In a heavy bottomed soup pan melt the butter and add the leeks. Saute them for about 5 minutes, or until they are completely wilted and translucent. Then add the mushrooms and sauté for another 5 minutes, or until the mushrooms have shrunk and become a darker brown.
3. Pour in the wine and scrape up any browned bits from the bottom of the pan. Once it is nearly evaporated add in the flour and stir for one minute. Then slowly whisk in the stock until there are no lumps left. Pour in the milk and add the salt. Feel free to add more salt to taste if necessary.
4. Simmer the soup for 5 minutes, then add puree it with a hand blender or in a standing blender. Serve warm, topped with the croutons.