Although I usually make pureed vegetable soups with a combination of chicken stock and water, I find that asparagus has an assertive enough flavor that you can make a full-bodied asparagus soup using only water as a liquid.
The trick in making water-based soups is to use as little water as possible: enough just to cover the vegetable so that it cooks evenly, but not so much that it has a thin, watery taste. Also, when I make a water-based pureed vegetable soup, I like to sweat the aromatics and the main ingredient in a very generous amount of butter or oil. This adds a little thickness and complexity to the soup, and allows you to avoid adding heavy cream to the soup at the end, which tends to blunt the flavor.
When I make a pureed green vegetable soup, I always throw in a little bit of spinach or arugula at the end and cool my soup in an ice bath to give the soup a nice bright green color.
At Duo or Olivea, when we have asparagus on the menu, we remove the bottom 2 inches of the asparagus stalks and save them for this soup. The bottom part of the stalk, which is usually whitish in color, has a lot of flavor, but it is also very fibrous; this means that it needs long, slow cooking to break it down and that when it is pureed, it needs to be passed through a strainer.
If you eat asparagus on a regular basis, cut off and freeze the bottom part of the stalk; when you have 2 pounds of stalks in your freezer, make this soup.
John Broening cooks at Duo and Olivea restaurants in Denver.
Asparagus Soup
Makes about 3 quarts, enough for about 12 servings
Ingredients
1/2 pound (2 sticks) unsalted butter
1 yellow onion, finely diced
1 bulb fennel, finely diced
Salt
2 bunches asparagus, cut into 1-inch pieces
1 cup dry white wine
Water just to cover
3 ounces fresh spinach, stemmed and washed
Pepper
Pinch nutmeg
Few shots hot sauce
Optional: olive oil and breadcrumbs for garnish
Directions
In a heavy-bottomed 1 gallon soup pot, melt the butter over medium heat. Add the onion and fennel and a pinch of salt. Sweat the vegetables until tender, about 10 minutes. Add the asparagus and another pinch of salt. Sweat until softened, about 10 minutes.
Add the white wine, and reduce by 2/3. Add water just to cover and simmer until the asparagus is soft. Add the spinach, and cook 1 minute.
Set up a clean 1-gallon plastic container in a bowl of ice water (cooling the soup in ice water will ensure that the soup stays green). Place a china cap or a fine strainer over the container.
Using a blender, blend the soup in batches until smooth. Pass through the fine strainer. Season the soup with salt, pepper, nutmeg and hot sauce to taste.
To serve, reheat the soup over medium heat, stirring often. Garnish with olive oil and breadcrumbs.
