Every good recipe starts wth the OED!
a. A ragout.
b. In full, ratatouille niçoise: a dish, originating in Nice, consisting of aubergines, tomatoes, onions, peppers, and other ingredients stewed in olive oil.
And
Fr.: the final element is app. f. touiller to stir up.
Ratatouille is, then, eggplant (aubergine being eggplant), plus other vegetables, stirred up. This sounds pretty accurate.
There are clearly all kinds of variations of ratatouille; you can alter any recipe to include whatever vegetables and degree of spiciness you want. I don't think you can call it ratatouille without eggplant, though, so keep in mind that if you hate eggplant, ratatouille is probably not what you want. A ragout of other vegetables would be good, though.
I tend to make very thick, chunky ratatouille, more like a bunch of mixed vegetables than a stew. That way you can eat it in lots of different ways: by itself, over rice, in an omelet. It's a really great breakfast food, actually; it's light enough that you can eat it right away upon getting up, and spicy enough to be interesting. And if you omit the cheese, which is just garnish anyway, it's vegan as well.
You need:
An eggplant. You want a firm, glossy one.
A zucchini or two, depending on how much you like zucchini.
Two or three ripe tomatoes.
A little tomato sauce, to even out textures and provide a base for everything.
Several cloves of garlic, diced fine. Use as many as you want.
Some yellow or white onion, diced fine, if you feel the need.
Olive oil in which to sauté things.
A saucepan and wooden spoon.
Cayenne pepper, basil, and salt and pepper, plus any other spices you want (thyme is good).
A block of good parmesan cheese, for garnish.
Optional: any other vegetables.
Chop the eggplant into half-inch cubes. Don't bother peeling it unless eggplant peel really bothers you. I tend to cut two or three round slices off the end, discarding any stem-oriented bits, lay the slices in a flat stack, then cut a grid into the stack. Voilá, perfectly cubed eggplant. You want a good two or three cups of this; use either half a large eggplant or a whole small one. If you feel the need for the eggplant to remain all white and pretty, you can sprinkle it with salt and lemon juice. Lemon juice is actually a nice thing to add to the whole dish, just be sparing with it.
Chop up the zucchini and tomatoes. I tend to cut the zucchini into smaller cubes, and the tomatoes into rough chunks (as they are going to reduce anyway), but you can do whatever floats your boat. I generally go for relative uniformity of size in the pieces of vegetable, to get a relatively uniform texture in the finished product. If you want to include any other vegetables--green or red pepper and mushrooms work well--chop them up as well. Set all these vegetables aside for a minute.
Dice the garlic as small as you can get it. I will use three or four cloves, usually, but increase or decrease according to how much you like garlic. If you want onions, dice them too. Then get out your saucepan, heat it up, and start sautéing your garlic and onion in enough olive oil to coat the bottom of the pan. I do this over fairly low heat, and stir often, to make sure they don't burn.
When things are looking soft and translucent, and the whole kitchen smells of garlic, add the eggplant. Sauté to soften, and to get the garlic flavor good and infused, then add the zucchini and tomato. If you are including any other vegetables, add them now as well. Add a bit more olive oil to keep things from sticking to the pan, then stir it all up and sauté until the tomatoes reduce.
Spice. You want lots of basil. Lots. If you can get fresh basil, so much the better: chop or shred it and throw it in. Use the cayenne fairly sparingly, at least at first; you can add more later if you want. The same goes for the black pepper, but you do want a good shake or two of salt, especially if you are in the off season for tomatoes. Ratatouille should not be sweet; the salt cuts the sweetness of the tomatoes. Add some other spices if you like. Oregano and thyme are pretty good, and a little lemon juice is interesting. Experiment and see what you like.
Add just enough tomato sauce to give the mixture a thick liquidy base. I would probably only use a few spoonfuls; you want the focus here to be on the vegetables themselves. Stir well to mix everything up, then cover and let simmer over low heat for ten minutes or so. Then give it a taste and see how you like the spicing. Add more of whatever you feel is necessary--I generally need more cayenne, as ratatouille is supposed to be rather hot--and let simmer again to mingle all the flavors.
When you think it's done, it is. Fill yourself a bowl, and grate some good parmesan over the top. Good!
Ratatouille will keep for a week or so in the refrigerator, and is just as good cold as it is hot. It might even be better after keeping a couple days, as all the flavors will be out in full force. Keep in mind, though, that it will get more spicy as it ages. Watch your mouth.