Vegetable soup is one of the most nutritious, low-fat, low-calorie dishes you can make. It's a great way to enjoy seasonal fresh veggies, as well as putting leftovers to good use.
And while a rustic soup, full of chunks of carrots, onions, potatoes and the like, is certainly appealing, it's not particularly elegant. That's where puréeing comes in.
Not only are puréed soups perfect for serving as a first or second course in a fancy meal, they're also great for getting kids to eat their vegetables.
Making Puréed Soups
Making puréed soups is as easy as using a blender. Well, as easy as making soup and then using a blender.
One of the wonderful things about puréed soups is that, since everything is going into the blender anyway, you don't have to be as fastidious about how you cut your vegetables. It helps to cut everything more or less the same size, so that it cooks evenly, but as far as how the pieces look, it doesn't matter.
An immersion blender will work, and it's certainly easier on the cleanup than a jug blender. But a jug blender will generally purée faster and more thoroughly. You might have to work in batches, depending on how much soup you're puréeing, and how big the pitcher of your blender is. But it's ultimately probably faster than an immersion blender, which, while convenient, always seems to leave some solid bits in the soup.
Puréed soups are a lot like classical sauces in the sense that they consist of a liquid plus a thickener. The liquid is usually broth, stock or milk, and the thickener is roux, which is a combination of butter and flour. With puréed soups, the liquid is broth or stock, and the thickener is the vegetables themselves.
Choosing Your Vegetables
Achieving the right consistency with puréed soups is easiest when using starchy vegetables like carrots, potatoes, sweet potatoes, squash, peas and corn, along with most any other root vegetable, like parsnips and turnips. Beans and legumes, including lentils and chickpeas, are also good starchy ingredients for making puréed soups. See this carrot soup, this turnip soup and this lentil-tomato soup.
In general, you would simmer these veggies in stock or broth, and as they cook, they release their starch into the soup. Then when you blend, your soup attains a nice, smooth consistency. The starch emulsifies, or holds the soup together. Without it, the soup would separate in the bowl, with the particles of puréed vegetable floating atop the liquid.
Non-starchy vegetables, like broccoli, cauliflower, asparagus, mushrooms, celery, tomatoes, peppers and leafy greens, are also wonderful ingredients for making puréed soups. But they need a little help in the thickening department. So you'll usually need to add some starchy ingredient to the soup, ideally one with a neutral flavor, like potatoes or rice. See this broccoli soup, this celery soup and this mushroom soup.
We'll talk more about thickening in a minute. But first let's walk through the process of making the soup. It's a standard method that you can use for making any kind of puréed soup, using whatever ingredients you desire.
Sweat the Aromatics
- Heat a small amount of butter or olive oil over low heat in a soup pot.
- Add some diced onions and garlic, cover the pot and let the aromatics cook for about five minutes. You're not sautéeing them, which is a high-heat method. This is called sweating, and the idea is to soften them without browning. The onions should be translucent.
- Next add a dry white wine such as sherry, vermouth, chablis, or chardonnay. Cook for a few minutes, until the wine is slightly reduced.
Add the Stock and the Veggies
- Now add the stock (such as white stock, chicken stock or vegetable stock) along with the main fresh vegetable ingredient of the soup. If it's a starchy vegetable, that's all you'll need. Otherwise, you'll need to add some peeled and diced potato—about 200 grams per liter of stock. But see below for other thickening ideas.
- Bring to a boil, then lower the heat and simmer until the vegetables are cooked and the potatoes are tender and can be easily pierced with a knife.
Purée the Soup
- Remove soup from heat and purée it in a blender, working in batches if necessary.
- Return soup to the pot and adjust consistency, if necessary, by adding more liquid.
- Return to a simmer. Hot cream may also be added now for extra creaminess. Adjust seasoning with Kosher salt and freshly ground black pepper, and serve with an appropriate garnish—such as some diced cooked carrot for a carrot soup, for instance, or a swirl of sour cream or creme fraiche, or some homemade croutons for crunch.
Alternate Thickening Methods
If you have leftover mashed potatoes, you can add these to your soup as a thickening agent in place of the raw potato. Likewise, you can add cooked rice, or even raw rice. A third of a cup of uncooked rice per quart of stock is about right. Simmer the soup until the rice is soft and then purée.
Frozen hash browns happen to make a wonderful thickener for puréed soups. Just chop them up and simmer them along with the other ingredients, then purée as described.
- Note that you can use this general technique for making soups that are fully vegetarian or vegan. Simply sub olive oil for butter, vegetable stock for chicken stock, and omit the hot cream at the end.
- Use care when processing hot items in a blender, as the hot steam can sometimes blow the blender lid off. Start on a slow speed with the lid slightly ajar to vent any steam, then seal the lid and increase the blending speed.
- Chopped fresh herbs may be added after blending, right before returning the soup to a simmer.