The most incredible thing about osso buco, the hearty Milanese dish of braised veal shanks, is how singular its flavor is given how simple it is. The braise itself contains little more than your classic assortment of aromatics, like onion, carrot, and celery; the shanks themselves; plus some wine, some broth, and maybe a little tomato. Those ingredients alone should produce a fairly run-of-the-mill braise—tasty but unremarkable. And yet, osso buco's flavor is unmistakable and superb, something you won't forget once you've eaten it for the first time.
The reason is twofold. First, there's the osso buco itself, the name (literally translating as "pierced bone") referring to the marrow bones in the middle of each crosscut shank. They contribute a tremendous amount of flavor as the rich marrow renders during the braise, basting the meat and infusing into the sauce. The second is gremolada, the dish's secret weapon. A mixture of finely minced lemon zest, parsley, and garlic, the gremolada is stirred into the braise near the end and also sprinkled on top as a garnish, adding a fresh, bright, and sharp kick. Together, these two features elevate osso buco to something extraordinary.
Making it starts with the shanks. Some restaurants and cookbooks call for mountainous hunks of meat, which looks impressive but comes with a couple drawbacks. First, it takes longer for the heat to penetrate and melt the tough connective tissue into tender gelatin, extending what is already a long cooking time. Second, it leaves you with servings so huge, it becomes a challenge to try to finish one; since the bone-in cut is impossible to evenly divide (who gets the marrow-filled bone?), splitting such a big section of shank isn't practical, either.
Too thin, though, and they'll curl and bend with the heat, leaving you with a saucer-shaped shank. Ideally, then, what you want are shanks no thinner than an inch and not much thicker than an inch and a half. That gives you a generous yet realistic portion size for each person.
Some people like to tie a length of butcher's twine around each shank, which can help hold the meat to the bone and prevent curling of thinner cross sections. My testing left me undecided on the benefit of this: The shanks I left untied didn't have any problems; meanwhile, some of the ones I did tie had the strings fall off as the meat contracted in the heat, and the others required snipping off the strings before serving, a small annoyance. It's possible that I got lucky with my batches and, if I'd continued testing untied shanks, that I'd have eventually discovered some fail rate. At the very least, I can conclude that the strings did no real harm, so if you don't mind taking the time to tie up the shanks and remove the strings later, it may be a worthwhile extra step. If you do mind, I wouldn't worry too much. The worst that happens is you have to reassemble a fallen-apart shank on the plate.
Next, the shanks are seasoned with salt and pepper and lightly dredged in flour, then browned in oil. You may find that a shank or two will have trouble browning evenly as the meat contracts around the bone—if it contracts enough, the bone can act like a tiny stand, with the meat hovering above the oil. Just do your best to push the meat down into the oil, and don't sweat it if a few shanks don't brown perfectly in every spot.
Once browned, the shanks are set aside, and finely minced aromatics go into the pot. The important thing here is to cut the vegetables into tiny pieces—they're going to melt and form the sauce, so if they're too big, you'll be stuck with a broth studded with vegetable chunks. I don't think that's ideal, especially since I use such a light dredging of flour. If you use more flour, the liquids will thicken more, but they'll also have a more muted flavor; less flour leaves the broth thinner, meaning finely minced vegetables can step in to thicken the sauce more fully. I like hand-mincing in situations like this, but if your knife skills aren't up to the task, or if your patience is limited, it's far better to throw the aromatics into a food processor and pulse them to a fine mince than to err on the too-large side. Save your chunky vegetables for another day.
When the minced vegetables have softened and are just starting to turn a light golden color, I add some hand-crushed drained canned tomatoes to the pot. Tomatoes are an optional ingredient in osso buco, but I like the flavor and texture they add. Still, I don't want one of those very tomato-heavy osso buco renditions that you sometimes see, so I drain and seed the tomatoes, using only the flesh.
The veal goes back into the pot along with any accumulated juices, plus dry white wine and some chicken stock. Beef stock might seem like the obvious choice here, but unless you have some homemade on hand, chicken is your best bet—it's versatile and, when store-bought, has better flavor than most of the beef broth options out there. If your stock is homemade and it has a naturally high gelatin content (you'll know because it will set like jelly when it's cold), you're good to go. If not, it helps to sprinkle some powdered gelatin onto the stock, allowing it to bloom for a few minutes before adding it to the pot. Even when hot and liquid, gelatin-rich stock has a thicker, more viscous texture that seems much richer than that of a watery broth.
A few sprigs of thyme and a bay leaf, and the whole thing goes into a low, 325°F (163°C) oven to cook. For the first couple hours, I use a parchment paper lid (see instructions here for how to make one). This slows down evaporation enough that the pot won't go dry too quickly, but still allows some water to cook off and the exposed surface of the meat to brown in the dry oven heat, leading to deeper, more complex flavor.
For the last hour,* I remove the parchment and let the braise brown more deeply in the oven. If it gets too dry, you can moisten it with more stock or water at any point.
* Remember, recipe times are almost always rough estimates: A variety of factors, from the meat to the oven to the pot used, can all affect how long it will actually take for the meat to become tender. Use the cooking times as an approximate guide, not as an absolute law. If your shanks need more time to get tender, give them as much as they need, adding more water to make sure the pot doesn't get too dry. That's real cooking—using your senses and adjusting as you go.
A couple teaspoons of the gremolada go in for the last 15 minutes or so, once it's become clear the shanks are tender enough. You can test this by trying to slide a fork into them: If it slides in easily, you're all set.
One traditional way to serve osso buco is with a golden mound of saffron-flavored Risotto alla Milanese. Slide a shank on top, spoon the sauce over it, and put it on the table. Everyone can sprinkle extra gremolada on top as a garnish, depending on how strong they want that flavor to be.
It's as classic and basic as a braise can get, and yet it's truly like no other.