French bistro fare is usually fairly predictable — that’s part of its classic appeal and charm. With few exceptions, steak frites is steak frites; a crème brûlée is a crème brûlée.

But there’s one bistro dish that comes in a near-endless array of variations, despite being described on most menus as “classic” or “traditional.” It’s a dish that ranks among the most relaxing comfort food, even though its ingredients and preparation methods can be the subject of heated debate. And with winter in full swing, it’s a dish that can now be found on almost every French menu in town (and on many non-French ones as well): the bean-based stew known as cassoulet.

“If you talk to 10 French chefs, they’ll tell you 10 different ways to make cassoulet that are indispensable,” the chef of the Stone Park Café in Park Slope, Josh Grinker, said. “You’ve got to include this ingredient, you must do this, you must do that.” As Mr. Grinker’s comment suggests, to explore the world of cassoulet is to encounter a sort of culinary Rorschach test. Everyone seems to know exactly how it should be made and insists that any other version is heretical, yet no two versions are alike. This is a rather fortuitous state of affairs for cassoulet non-purists (a category that includes this reporter), since almost every rendition is equally savory and delicious, and the slight distinctions from venue to venue provide a welcome element of variety without detracting from the dish’s essential strengths.

Let’s start with the basics: A cassoulet is a hearty, rustic stew of white beans, meat, sausage, poultry, and bread crumbs. The beans provide a creamy base for the assorted meats, and the bread crumbs add a crisp counterpoint, creating a harmonious balance of flavors and textures. The preparation, which dates back several centuries to the French town of Castelnaudary, is baked for several hours and is traditionally served in an earthenware vessel called a cassole, from which the dish derives its name.

As soon as you begin discussing ingredients, though, the picture becomes muddled. Some stipulate that the beans must be haricots; others say great northerns. Some say all the meat and sausage must be pork-based — usually some combination of slab bacon, pork rind, and garlic sausage — while others insist upon lamb. The poultry is usually duck confit (sometimes on the bone, sometimes not), but some use goose or chicken, or omit the fowl altogether. Even the bread crumbs are a point of contention, as some enthusiasts maintain that the crust must be broken, mixed back into the stew, and then allowed to reform up to eight times during the baking process, while others simply leave the crust on top.

These different schools of thought originally corresponded to distinct regional cassoulet styles in France, but most culinary authorities agree that the regional distinctions long ago became blurred and that the dish has taken on a lore of its own (helped along by nuggets such as the 19th-century writer Anatole France’s claim that his favorite restaurant had kept the same cassoulet pot simmering on the stove, with new ingredients periodically added, for 20 years).

“I’ve had customers tell me, ‘You put lamb in the cassoulet? That is not cassoulet,'” chef Jean-François Fraysse, a co-owner of the longtime Chelsea bistro La Luncheonette (130 Tenth Ave., 212-675-0342), said. “But I remind them that the southwestern part of France, where I’m from, has a lot of lamb, and that’s how we make it.”

The lamb in Mr. Fraysse’s version comes in the form of shredded lamb shank. He also includes hunks of pork sausage and a drumstick of duck confit with unusually crisp skin. It’s fairly close to the version considered indigenous to the French city of Toulouse, except Mr. Fraysse has taken the arguably sacrilegious step of omitting the bread crumbs.

“I regret that I don’t include them,” he said. “But so many people don’t eat bread now, so I have to make this concession for my American friends.” So this is what the Atkins revolution has wrought: a lower-carb cassoulet. Fortunately, the crispy duck skin provides enough crunch to make up for the missing crust.

Don’t tell that to the chef and owner of Lucien (14 First Ave., 212-260-6481), Lucien Bahaj, who’s very particular about the bread crumbs: They must be included, and the resulting crust must not be broken and reincorporated back into the stew. “If you do that, you lose the whole point of them,” he said, an unspoken “Duh!” plainly apparent even through his thick French accent.

Breadcrumb protocol notwithstanding, Mr. Bahaj’s cassoulet is fairly similar to Mr. Fraysse’s. The more unusual versions tend to be created by American chefs, like Mr. Grinker of the Stone Park Café (324 Fifth Ave. at 3rd Street, Brooklyn, 718-369-0082), whose cassoulet would scarcely be recognizable to a Frenchman. It features beans, lamb shank meat, and merguez, or spicy lamb sausage, but no poultry. No traditional crock, either: Each serving is molded into a puck and then served with a small lamb chop perched on top.

“We were actually looking for something to accompany a lamb chop,” Mr. Grinker said. “And then we thought, ‘Instead of potatoes or some other starch, why not a cassoulet?'” Like all of the other chefs interviewed for this article, he said the cassoulet was among his restaurant’s most popular dishes.

And does anyone complain about the unorthodox preparation?

“I’m sure a few people snicker under their breath,” he said. “But they haven’t told us.”