Turn Vegetable Greens and Herb Scraps Into Flavorful Pestos

Use up herb and vegetable leftovers for delicious sauces that can make many meals more interesting.


In my old, pre-coronavirus life, I aspired not to waste food, but I'll admit, I wasted a fair amount anyway. I may have intended to use up the rest of that ginger, or those herbs leftover from that recipe I made a few nights ago, or the bag of limes I was sure I needed for daiquiris that I ended up being too tired to actually make. I may have had noble intentions, but life often got in the way and eventually I'd have to toss my shriveled scraps in the compost.

Today is different. Almost overnight, quarantine living has forced me to become a more efficient home cook. It's also made it easier to be efficient—I'm home and I'm cooking every meal so I have every opportunity to make the most of what I've bought.

As I've detailed before, one of the main strategies I'm leaning on at home is what I'm calling "component cooking." I'm not really following too many fully fleshed-out recipes, but instead am building components: blanched or roasted or pickled vegetables; poached or roasted meats; cooked beans; and condiments aplenty. Then I'm mixing and matching them in as many ways as I can dream up, which keeps meals varied and interesting.

One very easy component we can all make with ingredients we probably have in our fridges are herb sauces in the style of pesto or chimichurri. They're endlessly variable and versatile.

A small dish filled with bright green fennel frond pesto
Fennel-frond pesto. Daniel Gritzer

Here's an example: This fennel frond "pesto" I made using the tops of four bulbs of fennel I'd bought. The bulbs themselves ended up in a rich bean stew. The fronds went back in the fridge. In my old life I would have found them there a week later, wilted and yellowing. But in this new existence I actually managed to do something with them before they went bad.

I picked the fronds and got about a quart's worth. Then I added some garlic cloves, some lemon juice and zest, a dollop of Dijon mustard, and a number of anchovies that almost bordered on being obscene. I topped everything off with a big glug of olive oil and blended it until I had more than two cups of sauce. Was it "pesto"? No, not really, but it had that kind of vibe.

It was bright and herbaceous and salty, and it was great spooned over the fennel and bean stew I made. It also made a really good pasta sauce, and was delicious swirled into fresh ricotta cheese as a snack. It was even better as a dressing for a salad of roasted carrots, fresh parsley, and sliced red onions. I didn't start out with a plan for how to use it, but it's been easy to find ways. It would've been killer tossed with a plain bowl of beans, but I'm all out now, so I'll have to try that with whatever herbal concoction and pot of beans I whip up next time.

A potato cake topped with thinly sliced roasted lamb and a roasted carrot salad with fennel frond pesto
For one dinner, I tossed sliced roasted carrots, parsley, and red onions with my fennel-frond pesto, then mounded them on top of a potato cake with thinly sliced roasted lamb. This wasn't a recipe, it was just a creative way to combine components I'd whipped up. Daniel Gritzer

Here are a few tips for making your own herb sauces with whatever you have on hand, whether during quarantine or any other time.

How to Invent Your Own "Pesto" Sauce

finished pesto in a marble mortar and pestle
Not every green herb sauce is pesto, but you get the point. Vicky Wasik

"Pesto" is in quotes here because not every herb purée is a pesto, just like not every soup is chicken noodle. But as a shorthand, it's probably the most widely understood way to talk about puréed, oil-based herb sauces.

Be Open to "Herbal" Possibilities

A variety of fresh herbs on a blue background
Vicky Wasik

When it comes to choosing herbs to turn into pesto, of course there are the obvious options like basil, parsley, and cilantro, but don't stop there. Chives, scallions, tarragon, and mint would all be great additions, as are fennel fronds and even carrot tops.

You can lean on softer herbs more fully without worry, like parsley or basil or fennel fronds. Others may be a little too assertive to be the only vegetal component. Woodsy herbs like oregano and sage could be tasty in moderation, but they might come across too aggressively on their own. Ditto for oniony scallions and chives. It of course depends how you use it, but it's often smart to cut very bold herbs and vegetables with more mild ones. Parsley, spinach, and even kale are all good picks for diluting a more pungent herb's flavor.

Alternatively, you could go all in on the bolder greens, but then be sure add less of the sauce to your food, or cut it another way (see eggs and nuts below).

One more trick that might come in handy is softening and taming the raw flavor of the greens or herbs by quickly blanching them in boiling water before shocking them in ice water and then puréeing (it even works for basil). You can blanch and blend most any herb or vegetable, but it's especially useful for tougher, fibrous ones like kale that can seem gritty when processed raw.

Go Nuts (Or Don't)

Side by side photos of toasted hazelnuts in a mortar and hazelnuts ground to a coarse powder in the mortar
Mortar and pestle not required. Vicky Wasik

True Genovese pesto wouldn't be pesto without pine nuts, and while you certainly don't need nuts for a flavorful herb sauce, they're an ingredient worth considering for their fatty richness and thickening abilities.

If you do add nuts, there's no need to limit yourself to pine nuts. Pistachios, almonds, cashews, walnuts, pecans, and more can work well. One thing to remember is that roasted nuts tend to be drier and may not blend up quite as smoothly as plump raw ones do.

Cheese Ain't a Bad Idea

adding Pecorino Romano cheese to pesto
Vicky Wasik

Once again, classic Genovese pesto serves as a template and its inclusion of finely grated hard cheeses like Pecorino and Parmigiano-Reggiano is another option worth considering. Cheeses add yet more richness and fattiness, but they also add complexity and their own form of tang, thanks to their lactic acid content.

Must you add cheese? No. But you probably won't regret it either. If you do, it's better to stick to harder grating cheese like Parm, though you may be able to purée in a soft and spreadable cheese like chèvre with good results. Just skip the semi-soft ones like cheddar and the soft-rind ones like brie.

Don't Sleep on Eggs

Pesto, pesto, pesto. I know, enough with the pesto. So let's look at another Italian classic: salsa verde from the Northwestern region of Piedmont. It's a parsley-based sauce that's served with many things, including bollito misto, a feast of boiled meats.

There's a lot that's great about salsa verde, from its salty and herbal capers to briny, funky anchovies. But perhaps coolest of all is the hard-boiled egg that often gets blended in. Sure, it gives the sauce a subtle eggy quality, but it's not obvious and I'd wager most blind tasters wouldn't pick it out. What it really does is help thicken and emulsify the sauce for creamier results.

Punch Up the Flavor

Small jar of anchovies in oil against white background.
Vicky Wasik

There's no way to list all the ingredients one might decide to add to a sauce like this, so I'll just rattle off a bunch off the top of my head. I'm sure you can think of more.

  • Citrus juice and zest (in particular, lemons and limes)
  • Capers and caper berries
  • Olives
  • Anchovies and tuna, or even a splash of fish sauce
  • Spices (black pepper, coriander seed, cumin, fennel, etc.)
  • Garlic and other alliums like shallots
  • Mustard
  • Chili peppers (fresh, dried, pastes, or pickled)
  • Some fresh or roasted tomatoes or bell peppers or rehydrated dried peppers (see romesco and pesto alla Trapanese for ideas)
  • Ginger

Watch Out for Acid

Acid in the form of lemon juice or vinegar can brighten up a bright green oil-based sauce. I added lemon juice in the fennel frond pesto I made. Do watch out, though, because heavier doses of acidic ingredients can turn bright green vegetables a duller army-green color, and you may lose some of that vibrant, fresh green flavor too.

Speaking of Oil

Olive oil is the real star in these sauces, its grassy green flavor pairing perfectly with whatever herbs and vegetables you're using in your sauce. But if you don't have olive oil, a fresh neutral oil (read: don't use that old sticky bottle you've been slowly drawing down for months) like canola, grape seed, or vegetable oil can all work. They won't add much flavor of their own to the sauce, but if you add enough other flavorful ingredients, that's just fine.

Get Creative

A bowl of pasta topped with pesto alla trapanese
Sicilian Trapanese pesto has tomatoes mashed in. It's still a type of pesto!. Vicky Wasik

Don't be afraid to experiment. Have an eggplant you don't know what to do with? Maybe roast it, scoop out the flesh, and mash that into your pureed herb sauce as well. It will be a totally different creation, but... why not?

Wondering if some green tomatillos might find a home in your sauce? Well it works in Mexico, so there's a decent chance you'll come up with something good.

Point is, take the time to look through your fridge and pantry, think about what you have and what it might taste like as part of your sauce. Really try to imagine the flavors and textures and how they might go together. You have better instincts than you may suspect, so take the risk. You may stumble on a genius idea.

It's Okay to Use a Blender

I have a history of blathering on and on about the wonders of the mortar and pestle, and I believe it as much today as I always have. But I'm also a very pragmatic cook, and it's important to remember that we're not always trying to create the absolute best-possible thing. Often all we really need is something tasty that we can use to make our meals more pleasurable while using up ingredients that might otherwise go to waste. If using a blender is the difference between you actually doing it and just thinking about it, please plug that sucker in and blend away.