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I've been religious about my ratatouille for years, telling anyone who would listen that the only way to make it well was by first cooking each vegetable separately, then combining them for a short simmer to briefly meld their flavors. It's a method promoted by many trusted cooks, from Julia Child to Jacques Pépin, and it's never delivered anything less than stellar results for me.
But there's a problem with being religious about just about anything, which is that a strict adherence to a single viewpoint often doesn't hold up when put to the test. I'd learned this lesson plenty of times before, and I've learned it once again thanks to my work on this ratatouille recipe. I was certain my test batches would confirm what I was already so sure of, but instead, I've come to realize that there's more than one way to make great ratatouille. That's good news for all of us.
I'm ready to put an end to my ratatouille proselytizing. You ready to join me?
What Is Ratatouille?
Before diving into cooking techniques, let's start by defining the dish. Ratatouille is a Mediterranean stew of summer vegetables that comes from the South of France (more specifically, Provence), though its reach extends far beyond that. Its exact origins are murky—Clifford Wright points out in his excellent and exhaustive A Mediterranean Feast that not only were tomatoes (a common ratatouille ingredient) not available in Europe until the sixteenth century, but La Cuisinière Provençale, an important Provençal cookbook from the nineteenth century, fails to include ratatouille among its 1,000-plus recipes. Even if ratatouille as we know it is a relatively new creation, similar vegetable stews have without a doubt been common in the region for ages, including relatives like samfaina from Catalonia and tombet from Mallorca.
While many variations exist, ratatouille typically includes a mix of eggplant, summer squash (i.e., zucchini, yellow squash, and other soft-skin types), onion, garlic, bell peppers, and tomatoes stewed in olive oil. Herbs vary, and some folks hold very strong opinions about which ones they should and should not be, but among the most ubiquitous are basil, parsley, and thyme.
I happen to own a great old cookbook called Vieii Receto de Cousino Prouvençalo (Old Recipes of Provençal Cuisine), which is written in both Occitan and French, and it has one of the simplest recipes for ratatouille one could hope to find. It says to add zucchini, bell peppers, and peeled eggplant, all cut into long strips, to a pot with diced onion and a few cloves of garlic and cook them together over a low flame with olive oil.
On the other end of the spectrum are more complicated approaches, which call for steps like pre-salting the eggplant and squash to drain them of excess moisture, cutting each vegetable into small cubes, and cooking the vegetables individually before combining them in a single pot; aromatic additions like a bouquet garni (herb bundle) come up often.
One thing is certain: While you can make ratatouille year-round with vegetables from the supermarket and get pretty good results, nothing compares to making it with summer produce at the peak of ripeness, when bell peppers are shockingly sweet and garlic, not long from the earth, exudes a sticky oil when you cut it.
Approaches to Cooking Ratatouille
At its heart, ratatouille is a rustic dish, designed to make use of all the produce that's abundant this time of year. Ease and simplicity are key—no one wants an overly laborious recipe when the main objective is to keep pace with the summertime onslaught of tomatoes, eggplant, and squash. Just as key, though, is making the most of those ingredients. Which means we still have to decide a few things about how to approach the recipe.
Cutting the Vegetables
Perhaps the first decision is how to cut the vegetables. A lot of recipes, especially the more rustic ones, call for larger pieces, but I'm pretty firmly in the small-dice camp. Primarily because I think it significantly improves the eating experience: When the vegetables are small enough, every spoon- or forkful will contain a good mix of each, delivering the biggest wallop of well-rounded ratatouille flavor. Plus, smaller pieces have more surface area, which can help speed cooking (and therefore flavor development) and allow for more thorough seasoning.
I have yet to meet a large-cut ratatouille I've loved. Those boulders of slightly bland zucchini and eggplant just don't do it for me. It takes more time to dice everything more finely, but it's one step that I really think is worth it. Anywhere from quarter-inch to half-inch pieces is a good size.
I'd never before bothered with pre-salting my eggplant and squash for ratatouille. Because I dice my vegetables small, I'd always figured the increased surface area alone was enough to quickly drive off excess moisture, making the salting step unnecessary. Still, it's called for in a lot of recipes, so I cooked up two batches, the only difference between them being that I'd pre-salted the eggplant and summer squash in one and not in the other.
To my surprise, this step had a bigger impact than I was expecting. The salted eggplant and squash produced ratatouille with more depth and sweetness. The difference wasn't extreme, but, at least when I tasted the two batches side by side, it was noticeable. One possibility is that when you remove some of the water content in advance, less energy is spent evaporating that moisture in the pot, which means that the sugars in those vegetables can concentrate and caramelize more quickly and thoroughly.
The effect isn't drastic enough for me to say that you absolutely must pre-salt those vegetables—if you don't have time, go ahead and skip it. If you plan your knife work efficiently, though, you can dice the eggplant and squash, then salt them and let them sit while you continue dicing the other vegetables, with little extra time added to the recipe at all.
In case anyone is wondering whether those drained juices from the pre-salting are flavorful enough to warrant reincorporating into the dish, I'll tell you that I tasted a spoonful, and they tasted like very little except for salt. Dump 'em.
Single-Pot Versus Individually Cooked Vegetables
Here's the part that I've always been convinced makes the biggest difference between merely good ratatouille and great ratatouille. Why? First, because each vegetable cooks at a different rate and absorbs different amounts of oil. Bell peppers and onions take longer to cook than squash and eggplant, for instance, and spongy eggplant is way more of an oil trap than the denser vegetables. By cooking them separately, you can control the doneness of each one with more precision, leading to a finished ratatouille that manages to meld their flavors while also maintaining their individual textures and tastes. Plus, cooking each vegetable individually means that they get more face time with the hot pan, which should aid in flavor development. (Compare this to the steaming/stewing that takes place when they're all dumped in a pot together.)
In my tests, though, I found that while the above is true—you do preserve the shape and flavor of each vegetable a little better by cooking them separately—the difference was not nearly as great as I'd anticipated. As you'll see in the photo below, the cooked-separately batch (at right) contains more discrete individual pieces of each vegetable, while the cooked-together batch shows more breakdown among the eggplant and squash pieces.
But they aren't wildly different—not in taste, and not in texture. In the end, I had to conclude that cooking the vegetables separately makes a small difference, which is worth doing if you really value keeping each vegetable more distinct, but not absolutely essential.
If you have a good sense of the relative cooking times of your vegetables, it's also possible to do a hybrid of the two methods. In that case, what you'd do is add each vegetable to the pot in a sequence based on roughly how long they need to cook, starting with the onion and garlic, then adding the bell peppers soon after, followed by the squash and eggplant, and finally the tomato. It's not as accurate as cooking them individually, but it's still a little more tailored to each vegetable's need than the one-pot method.
A few things worth noting: First, I didn't test larger vegetable pieces, and it's possible that you'd see a bigger difference between one-pot and separately cooked versions in that case. I'm just wedded to using smaller pieces, so it wasn't a question I cared to explore, but it's worth considering if you cut your vegetables larger.
Second, while the individually cooked approach requires more of your attention, don't assume that it also requires more of your time. Sautéing each vegetable one after another certainly stretches the process out, but if you're comfortable juggling multiple pans at once, you'll actually reduce your total cooking time compared to the one-pot approach.
Third, some of you may be wondering whether there are any browned bits on the bottom of the skillet that would be worth collecting by deglazing and then adding to the final pot of ratatouille. To find out, I deglazed my pan with water after sautéing each of the vegetables, let it reduce down to just a few tablespoons, and tasted it. Turns out, it tastes like very little. Skip it.
Fresh Diced Tomato Versus Tomato Purée
The last big question for me concerned the tomatoes. It's the peak of summer, so you have your pick of fresh, seasonal tomatoes to use, which you can dice and cook into the dish. Alternatively, you can make a purée of cooked tomatoes, either from fresh or by crushing or blending canned ones and adding that to the pot.
I tried it both ways, and the results are striking. You can immediately see the difference—despite plenty of cooking, the diced fresh tomato maintained its shape to the end, while the puréed tomatoes acted as a sauce, coating everything in a red sheen and helping to bind it all together. As you can imagine, the tomato flavor is more pervasive when added as purée, since it glazes every other vegetable in the dish.
Once again, this comes down to personal preference: If you want a more lusty, tomato-tinged ratatouille, the purée, whether from canned or fresh tomatoes, is a no-brainer. If you want the other vegetables, like the eggplant, to shine through more, go with diced fresh tomatoes. I prefer the purée, so that's what I've called for in my recipe.
Ratatouille: Step by Step
I start by salting the eggplant and squash and letting them stand in a strainer set over a bowl for between 15 and 30 minutes.
Whether doing the individually cooked or the one-pot approach, I then sweat onion and garlic in olive oil. For the one-pot approach, the next step is to combine everything else in the pot and let it cook until done.
For the individually cooked approach, as each vegetable finishes cooking, I transfer it to a baking sheet to cool slightly. Spreading the pieces in a thin, even layer allows them to cool more evenly.
I repeat this with the remaining ingredients.
As each finishes, I scrape whatever is currently on the baking sheet into a pot and spread the next vegetable on the sheet to cool a little.
Once everything is in the pot, I set it over low heat and add the tomato.
I also add herbs at this point; here, it's a bundle of basil, parsley, and thyme.
Herb garnishes are up to you, too. In these photos, I've stirred in some chopped parsley, but you could use basil, another herb, or just leave it out altogether. I'll often also stir in a bit more fresh olive oil for flavor at the end.
When it's all done, there actually is one point on which I maintain my religious feelings: As good as ratatouille is hot, it's so, so much better when eaten slightly chilled or at room temperature the next day.