One Wednesday evening, there was a knock on my door. “I made bouillabaisse,” my neighbor said, holding out a large bowl of ruddy, saffron-scented stew. “I was missing my mom… but it’s probably not bouillabaisse because I was out of potatoes and only had salmon.”

After I brought it inside, I had a spoonful. It was silky and soft, slightly sweet, and deeply savory. I ate the entire bowl while standing at the counter.

I knew that my neighbor’s mother, Maryline Parca, grew up in a town not far from Marseille, the French port city that calls bouillabaisse its own. The next time she came to visit, I pressed her for more information. “It’s not my recipe,” Maryline, who now lives in San Diego, told me. “It’s from an old cookbook. And I don’t know if I follow it exactly,” she said, laughing softly. “I use salmon, because I like salmon, but that’s not traditional at all. I always add white wine, but I know some people use Pernod or something with that flavor… And I know they say to add fennel, so sometimes, sometimes, I add fennel seeds… I would only use fresh tomatoes, but people do use canned…”

What ensued was an amusing conversation about traditional recipes and the traditions family cooks establish and pass on. Today’s recipe, like Maryline’s, is a bouillabaisse that strays from tradition for the sake of home cook flexibility.

For many decades, the Marseillais successfully scorned copycats, insisting that bouillabaisse could be made only by them, in their town, with their fish.

By 1980, a group of restaurateurs in Marseille had signed a charter to establish a set of standards for bouillabaisse. According to the document, the dish must contain four different species of fish (cooks may choose from a longer list of local options), olive oil, onion, fennel, tomatoes, potatoes, garlic, saffron, parsley, salt and pepper. It is to be accompanied by croûtons — slices of well-toasted bread, not cubes or torn chunks — and rouille, a spiced aioli.

Less a recipe than a prescription, the charter is not especially well known among home cooks. What is widely accepted is that the dish was probably invented centuries ago, back when Marseille was a Phoenician city. It’s said that it was a way for fishermen to turn scraps (or, some say, choice morsels) from their daily catch into dinner for their families.

So we’ve come full circle. No-frills weeknight cooking to froufrou restaurant fare to, once again, get-it-on-the-table weeknight cooking.

After she’d returned home to San Diego, Maryline mailed me a photocopy of the recipe she consults when she makes bouillabaisse. It’s from late chef Henri-Paul Pellaprat’s “La Cuisine: Familiale et Pratique,” and it includes leeks in addition to onions and garlic, white wine, and water. It contains neither fennel nor potatoes. What it does specify, as Maryline translated into English in a note to me, is “small fish with firm flesh and also some whose softer flesh, dissolving while cooking, will slightly thicken the broth.” That, I discovered after testing several recipes, is what makes a bouillabaisse so unforgettable. It’s what makes bouillabaisse, bouillabaisse.

In a good version, the broth has a satiny viscosity, like a thin cream. When chefs started making it at their restaurants, they added fumet, a seafood stock that can take hours but is rich in gelatin, an effective emulsifier. This, in combination with the tomatoes, water and olive oil, results in a smooth, full-bodied broth.

Though homemade fumet will add lovely flavor and instant silkiness to bouillabaisse, it’s not necessary. What you’re looking for is a gentle emulsion between the olive oil and other liquid (tomatoes, water and/or wine), and using fattier or softer-fleshed fish, such as salmon, hake or tilapia, makes that happen just as well. Simmering potatoes with the onions helps, too. This recipe, inspired by the one my neighbor made me, plus those of her mother, Pellaprat and others, may lose points with those in charge of enforcing the bouillabaisse charter.

No matter: It’s a marvelous meal that can be on your table in an hour.

Weeknight Bouillabaisse

This variation of bouillabaisse, the vermilion-hued French seafood stew, is simplified and flexible so you can get it on the table faster. There are many ways to make it, but the residents of Marseille generally agree that it should contain several types of fish cooked in a broth with onions, garlic, fennel, tomatoes and saffron. Many bouillabaisse recipes call for a thick seafood stock, and rouille, a sauce similar to a spiced aioli that is served on the side, both of which make the recipe labor-intensive. This version skips both of those components.

A mix of different seafood is ideal, but even just one kind of the freshest, local fish you can find is fine. In France, bouillabaisse will almost always be served with slices of well-toasted bread (croutons in French), for soaking up the flavorful broth. At home, you can serve it with or without bread, toasted or not.

Storage: Refrigerate for up to 2 days.

Where to buy: Saffron can be found at spice shops, well-stocked supermarkets and online.

4 to 6 servings (makes 10 cups)

8 ounces shellfish, such as mussels (debearded, if needed) or small clams, such as littlenecks (optional; see Substitutions)

3 tablespoons olive oil, divided

2 tablespoons unsalted butter

2 leeks, white and light green parts only (8 ounces total), trimmed, cleaned and thinly sliced

1 medium yellow onion (8 ounces), halved and thinly sliced

1 small fennel bulb (4 ounces), thinly sliced, a few fronds saved for serving (optional)

6 garlic cloves, minced

1 teaspoon fine sea salt, plus more as needed

1 1/2 cups dry white wine, such as sauvignon blanc or pinot grigio

1 pound yellow potatoes, peeled if desired, and cut into 1/2-inch pieces (optional)

4 cups water or seafood stock, plus more as needed

4 to 5 ripe plum tomatoes (1 pound total), coarsely grated

Pinch saffron threads

1 pound fish, such as rockfish, halibut, hake, tilapia or salmon, deboned and skinned, if desired, and cut into 1 1/2-inch pieces

Freshly ground black pepper

5 tablespoons finely chopped fresh flat-leaf parsley, divided

4 to 8 (3/4-inch-thick) slices baguette, French country loaf or sourdough, toasted

If using clams, while you prep the rest of the soup, soak them in a deep bowl of cold water, so they can discharge any grit.

In a large lidded pot or Dutch oven over medium heat, heat the oil and melt the butter. Add the leeks, onion, fennel bulb, if using, garlic and salt. Cook, stirring occasionally, until the onion and leeks soften and turn translucent, 6 to 8 minutes.

Increase the heat to high, and stir in the wine. Bring to a boil and cook until reduced by half, about 2 minutes.

Add the potatoes, if using, water, tomatoes and saffron, crushing it between your fingers as you sprinkle it into the pot. Give everything a good stir, cover the pot and return the liquid to a boil. Leave the lid very slightly ajar and cook, stirring occasionally to ensure nothing is sticking to the bottom of the pot, until the potatoes are easily pierced with a fork, 15 to 18 minutes.

Reduce the heat to medium. If you have added the potatoes, they will have absorbed a lot of the seasoning, so taste the broth, and season with more salt, if desired. If using clams, drain, and discard any that do not close when gently tapped. Add the shellfish and/or fish and, if they’re not submerged in the liquid, add additional water to cover by 1/2 inch. If using only fish, simmer uncovered until it’s cooked through, 1 to 3 minutes, depending on the type of fish. If also — or only  using shellfish, cover the pot and cook until the mussels or clams open, 2 to 3 minutes. (Discard any mussels or clams that do not open.)

Remove from the heat. Taste the broth, and season with more salt, if desired, and a few turns of freshly ground black pepper. Add 2 tablespoons of the parsley, and very gently stir to combine, taking care not to break up the cooked fish. Divide among individual bowls, garnish each with a few fennel fronds, if using, and the remaining parsley, and serve, with the toasted bread slices for dipping into the broth.

Substitutions: Leeks add a unique flavor to this dish, but you could use more yellow onion if that’s all you have. If you don’t have shellfish, use more fish. Instead of fresh fennel you can use 1/2 teaspoon toasted fennel seeds, added with the onions and leeks. Alcohol-free? Use nonalcoholic wine, or 1 1/4 cups water and 1/4 cup white wine vinegar. (You may need to add more vinegar to taste.) If you can’t find ripe tomatoes, use one (15-ounce) can crushed tomatoes. No saffron? Skip it.

Nutrition per serving (1 2/3 cups), based on 6 | 440 calories, 33g carbohydrates, 68mg cholesterol, 18g fat, 3g fiber, 25g protein, 5g saturated fat, 570mg sodium, 4g sugar