Ratatouille was one of the very first dishes I ever learned how to cook. Or so I thought. The year was 1995, the location was my holding-hands-type-girlfriend's parent's house just north of the city, and I had an eggplant in my hand which I was—under her instruction—cutting into largish chunks to be deposited directly into a simmering pot of a rich, onion-packed garlicky tomato sauce on the stovetop.
It wasn't until a few years later that I realized that what we were actually making that day was simply a very primitive form of but one of the many versions of ratatouille.
Truth is, when it comes to ratatouille, there's no real agreement on even exactly what it should be, never mind how to make it. It originates from Occitan cuisine, the unique cuisine of modern-day Provence and a few surrounding areas in Mediterranean France that has obvious Catalan, Italian, and French influences.
The only thing that most recipes do agree upon is the ingredients: tomatoes, garlic, and onion form the base sauce, while eggplant and zucchini are the main vegetable elements, with the occasional bell pepper or summer squash thrown in. The aromatics consist of local herbs—thyme, marjoram, basil, or savory (among other possibilities)—and of course, plenty of good olive oil.
While the ex-girlfriend's stew-everything-together-into-a-thick-sauce version has plenty of precedents and is delicious in its own way, after spending many summer experimenting with different versions of the dish, I've settled on what I believe to be the most summery of the lot.
The technique used is one advocated by both Julia Child and Joël Robuchon, who, in his book, claims that "the secret of a good ratatouille is to cook the vegetables separately so each will taste truly of itself." Rather than stewing ingredients together and melding flavors, ratatouille is about keeping flavors distinct so that each bite will be fresh and exciting.
To build up a flavorful base, start by slow-cooking sliced garlic in olive oil then infusing it with sweet, mild garlic flavor before adding fileted tomatoes and thyme. If you have really really good fresh tomatoes, go ahead and use them. I usually go with whole canned tomatoes, as they are superior in flavor to the supermarket variety.
After that, I sauté onions, followed by zucchini, summer squash, and eggplant, all finely diced, all cooked separately and in succession in the same skillet. The key to the zucchini, squash, and eggplant is to cut them small enough that you can completely cook them through before their exterior starts to overcook and get mushy. Bright colors and summery flavors are what you're looking for here!
Finally, with all the ingredients sauteed, it's a matter of tossing them together. For a long time there was something missing from my ratatouille and it took me a while to realize: with such a relatively small amount of tomato to other vegetables, the dish was lacking in acid. A quick squeeze of lemon juice (along with some zest) right at the end bring it all into sharp focus.
Ratatouille is great as a side dish on its own, perhaps spooned onto good toasty bread. It can be used as a sauce for fish or chicken or other vegetables. The easiest way to enjoy it is as a full meal, in a big bowl of pasta.