If there's one thing I learned the hard way in culinary school, it's that the simplest looking elements—a side of home fries, a whole roasted chicken, chopped herbs—tend to put you in your place the first time you attempt them under the supervision of a professional chef.
"Vegetable purée," I thought, on the first-ever go-round. "You cook the vegetables; you puree the vegetables. Got it."
Oh, silly, silly me. While it seems impossible to botch, and most imperfect versions—while they may be too thick, chunky, soupy, or flavorless altogether—are certainly edible, a creamy vegetable purée can take some know-how.
Lucky for you, secrets are not my forte. Here's what I know.
The Secrets to Smooth, Pretty Purées
The techniques for puréeing may vary slightly depending on whether you're working with a root or starchy vegetable (like potatoes or starchy squashes), a stringy or fibrous vegetable (celery, spaghetti squash, or anything with an outer shell like peas or beans), or a highly absorbent veggie such as eggplant. But there are some general rules to heed.
Most vegetables will yield smoother purées if they're fully cooked before being mashed, blended or processed, and if all firm or fibrous parts such as skins or seeds are removed at some point along the way. To achieve even cooking, be sure to prep the vegetables into small, even-sized pieces if applicable: They'll cook at the same speed, and your blender (or food mill, or own two hands) will have an easier time smoothing them out later.
If you are making an especially thick purée or have a relatively weak blender, you may need to press down on the solids to get them in contact with the spinning blade. To do this, run the handle of a large metal ladle through the hole in the lid of the blender before attaching it to the jar. Once things get moving, use the bottom of the ladle to push foods down into the blades. The rounded shape of the ladle will prevent it from getting caught in the blades, even if you accidentally make direct contact, so don't worry.
Do note that it's not all about the texture, though—flavor and color are top priorities, too, so be sure not to overdo it on the initial cooking. Keep in mind any carryover cooking that could happen during the puréeing, especially when dealing with green vegetables, which can quickly go from bright green to a sad olive-gray. Basically, cook the foods to the point at which you'd like to eat them.
"the final phase of almost all purees involves adding in a little butter or oil for richness and flavor"
Finally, the final phase of almost all purées involves adding in a little butter or oil for richness and flavor, as well as cream, stock, or another liquid (water, liquor, vegetable juice etc) for consistency. If you're using a blender or food processor to do your handiwork, you can drop the butter (room temp works well) and liquid (always warm them to keep the puree warm) right in. If you're using a masher or mill, just stir the dairy or any liquid in at the end.
One word of warning: Hot foods can rapidly release a lot of hot steam when you purée them, blowing the top off your blender. To avoid ugly accidents, allow your food to cool slightly and only purée a small amount at a time. Firmly attaching the lid and holding it down may seem like a good idea, but don't do it—trapped steam will expand inside and forcefully blow the lid off. Instead, leave it slightly cracked (hold a kitchen towel over the open space—if the lid has a vent in the center, keep it open) to allow room for expanding steam to escape.
And if your blender gives you the option, start out slow, and slowly increase the speed once it gets moving.
I won't lie: I like to keep it simple, so I tend to steer clear of these more stubborn veggies when making purées and stick to the "Everyone in the blender!" approach. But, if you're simply dying for a rhubarb or a celery purée, there are some things to keep in mind. These vegetables, too, should be cooked to the softest point you can get them without waterlogging them, draining the color from them or zapping their flavor.
Still, most will hold on to some of their rougher parts even after being pulverized into a purée. What to do?
Start by removing as much tough fiber as possible before you even begin. Peel celery stalks, and remove seeds and fibrous innards from other vegetables.
Once they've been puréed, ensure their smoothness by passing them through a medium mesh sieve. You can use a drum sieve (a.k.a. a tamis—those big, circular screens with the metal or wooden wall around the edge) by working a scoop at a time, pressing the purée through the mesh with either a large pestle, a pastry scraper, or the back of a spoon or ladle. Alternatively, use a bowl-shaped or conical strainer set in a large bowl, pressing the solids through with the bottom of a ladle.
Stir in any any cream or butter to your purée at the end.
A Watery End
As for those uber-absorbent veggies we spoke of (such as eggplant), you can basically follow the steps above. One exception to note: These moisture-eating vegetables should be cooked in a dry-heat fashion (baking or sautéing) rather than being boiled, so they don't fill up with liquid. You can also try puréeing these by streaming in oil, which will help emulsify them into a thicker consistency than a water-based liquid like stock or cream would.
In puréed form, these tend to make a delicious side dish and, in my opinion, a great alternative to a plain old starch like rice. Not to mention, they're some of the easiest to handle, since they tend not to have seeds and are easy to peel.
"Heat those babies until a toddler could smoosh one with his fingers"
The only secret here: cook. the vegetables. fully. Not so they're al dente, or just barely fork-tender. Heat those babies until a toddler could smoosh one with his fingers—until they're fully soft all around, but not yet waterlogged or mealy.
Once they're fully cooked (you usually have your choice to boil, bake or steam) most root vegetables can be puréed in the blender or food processor. The ones to avoid include potatoes and some starchy squash, since spinning these through a machine will turn them into a sticky, gluey mess. Pass these through a food mill or hand-mash instead. Then mix in any warm cream or butter.