In a departure from standard recipe-writing protocol, I'm including the ingredients and instructions exactly as written in the book, with the sole purpose of showing the nature of its recipes. In practice, however, I did saute the leeks and onions first in some oil, before continuing with the recipe as written. The cooking technique here is basically a slow-cooker process — dump everything in and heat it up — which means that if your stove is full up with other soups that need hovering over on your Soup Night, you can easily make this in a slow cooker. The soup is simplicity in itself, and is prime for all kinds of toppings and add-ins, such as chopped nuts, crushed red pepper flakes (which I used in the photos), croutons, pepitas, parmesan crisps or a drizzle of sriracha. This soup is also super easy to veganize without losing a lick of flavor: just substitute vegetable broth for the chicken broth, and coconut milk for the dairy.
Combine the leeks, onions, cauliflower, bay leaves, and chicken broth in a large soup pot and bring to a boil. Reduce the heat and cook, covered, until the cauliflower is tender, about 10 minutes. Remove and discard the bay leaves.
Add the hot milk, salt, and pepper, and transfer the soup to a blender (careful, it's hot) and puree until smooth, then return to the pot. Or use an immersion belnder and puree the soup right in the pot.
Serve hot with a sprinkling of cheese or your other favorite topping.