Don't get me wrong: I've got nothing against cream soups. Cream of mushroom. Cream of spinach. Cream of chicken. I love all of them from time to time. But the thing about cream soups is that dairy fat has a way of coating the tongue and dulling vegetable flavors. A cream of asparagus soup might taste like rich, creamy asparagus, but you'd never describe it as bright. If you want a really bright yet creamy vegetable soup, you've got to get rid of that dairy fat.
So how do you make a super-creamy soup with no cream at all? There are a couple ways to get there. Sometimes I'll use bread to thicken my soups, as in this 15-Minute Tomato Soup. The other technique is using a classic French preparation called velouté. The word comes from the same root as velour, and, just like a neon velour tracksuit, velouté is smooth, suave...let's just go with velvety and bright.
In classical French cuisine, velouté is technically a sauce made by thickening stock with a butter- and flour-based roux. Think béchamel with stock instead of milk. These days, if you see the word on a menu, it's more often than not referring to a velvety, satiny soup with relatively little to no dairy fat.
I start my asparagus/tarragon version by sautéing aromatics in olive oil. For sweet asparagus, I prefer the mild flavor of spring leeks to onions. Celery or garlic might be common choices here as well, but I decided to use a thinly sliced bulb of fennel in order to reinforce the anise flavor of the tarragon.
I sauté the vegetables with a pinch of salt in order to help draw out moisture, then, once they're fully softened, I add a couple tablespoons of flour, stirring it until it's blended with the oil in the pot. Next, I pour in a few cups of chicken stock. You could also use vegetable stock, but make sure to use a homemade one; store-bought vegetable stock is almost universally terrible.
Once it all comes to a simmer, I add some chopped asparagus and a handful of minced fresh tarragon leaves. I tried making a version of the soup in which I sautéed the asparagus before adding the stock, but I found that it didn't really offer a flavor advantage, and resulted in a soup with duller color.
To make things extra fancy, I like to pull out a few asparagus tips after just a minute of simmering, when they're still bright green and crisp. They make a great garnish for the finished soup. I continue simmering the rest of the asparagus until it's tender, just a few minutes longer, then hit it with a squeeze of fresh lemon juice to brighten it up.
If you want it perfectly velvety-smooth, you can transfer the soup to a powerful countertop blender and let 'er rip, passing it through a fine-mesh strainer afterward. If a still-pretty-smooth-but-a-little-more-rustic purée is okay by you, then a good handheld immersion blender will do the trick, with the added advantage that you can purée the soup right in the pot. (Just be careful of splash-back. I coated my counter and shirt in green slime, Double Dare–style, at least once while developing this recipe!)
Like fresh asparagus itself, this soup is one of those that are best eaten right after they're made. It cooks so quickly that the purée should still have a vivid green color. It'll still taste fine if you chill it and serve it the next day, but it'll dull to a drab yellowish green by the time you've reheated it.
I like to garnish my soup with more chopped tarragon, some of the wispy fronds from the top of the fennel, the asparagus tips, a drizzle of olive oil, and just a touch of crème fraîche.
Okay, so I guess crème fraîche is technically dairy fat. Sue me.