Charm Your Valentine With This Old-School French Seafood Recipe

I’m admittedly narrow-minded when it comes to lobster: I want to eat them whole, shelling them at the table, and dipping the meat in drawn butter, or I want a lobster roll. Almost no other lobster preparation interests me nearly as much because I want as little as possible to get between me and my lobster. But I’m opening my mind to lobster thermidor, the old-school French preparation that dates back to the late 1890s and is named for a controversial play called Thermidor that dramatizes the end of the Reign of Terror during the French Revolution. And if I’m being totally frank (and not totally modest), the biggest breakthrough in my enjoyment of lobster thermidor has to do with how I make it—reinforced with a quick and easy lobster stock so that every bite is an explosion of lobster flavor.

There isn’t any one “official” recipe for lobster thermidor, and the specifics of how it’s made have changed over both time and place, with French versions differing slightly from American interpretations. If I were to try to define it, it’d be something like this: Halved lobsters that are stuffed with their own cooked meat, which has been dressed in a creamy, roux-based sauce featuring some kind of stock, cheese, a dash of mustard, plus other flavorings.

Lobster thermidor shares similarities with other French and French-inspired lobster dishes like lobster à l’Américaine, Newburg, cardinal, and mornay, but if I were to try to sketch out the details that collectively distinguish it in one way or another from the rest, they are:

• The presence of mustard in thermidor sauce, which the others typically lack
• The presence of cheeses like Gruyère and Parmesan, which cardinal, Newburg, and à l’Américaine lack
• Less tomato than the typical sauce in à l’Américaine
• The final gratinée (broiling) step, which not all of the others share

It’s not clear-cut, and you can find renditions that break one or more of the rules above, but generally speaking, if the dish has lobster broiled in its shell, and includes mustard and cheese in a roux-based sauce, it’s probably thermidor.

Now let’s talk about that cheese.

Seafood Plus Cheese? Yes, Please

There’s a rule of thumb in Italian cooking that says seafood and cheese should never be combined. You have to love the French for gleefully thumbing their noses across the border with dishes like this, which unapologetically blend not just French cheese in the form of Gruyère but also Italian cheese in the form of Parmigiano-Reggiano with the shellfish. And you know what? It’s great.

I can imagine that there are more than a few people out there, some possibly reading this right now, who have accepted the Italian no-cheese rule as some kind of semi-religious doctrine. I would recommend they consider that this isn’t a rule that needs to be absolute, and while it’s advisable to approach the combination of seafood and cheese with caution—because, yes, they often do clash—they can also work well together. Even in Italy the rule is at times broken; for example, Sicilian involtini di pesce spada (swordfish rolled with seasoned breadcrumbs) is sometimes made with pecorino.

Lobster thermidor is a recipe where the cheese, which is both melted into the sauce (mornay-style) and also grated on top for the final broiling, adds richness and depth.

Go Big or Go Home

I, as a self-proclaimed human garbage can, am not a good measure of how much food is “enough.” Case in point: At the photo shoot for this recipe, I told everyone it served two. My colleagues looked at the platter of overflowing lobster, then back at me, then back at the platter, with clear concern for my judgement. Okay, I allowed, it can probably also serve four.

Let me be clear: This recipe definitely serves four. (Ah, a moment of personal clarity around serving portions, it’s nice on those rare occasions when it happens.) Does that mean two very hungry, very passionate lovers of lobster couldn’t eat all of this in one sitting? I know I could, but I’m me, and I’m weird and probably not who you should be basing this kind of decision on.

Even if you love eating lobster as much as I do, you can still probably share this recipe four ways, and that’s because—lobster glutton that I am—I pack three lobsters’ worth of meat into the two split shells, which is one lobster more than I’ve ever seen any other thermidor recipe do (even when they serve four!). I have a couple very legitimate reasons for this that extend beyond my own penchant for eating.

First, a third lobster provides us with extra shell, which I put to good use by making a quick lobster stock that significantly improves this dish. That alone is a worthy reason. Second, if you do split this recipe four ways, that extra little dose of meat from the third lobster gives each serving a pile of meat that feels generous and gratifying, not skimpy, which is important for a dish that feels so triumphantly celebratory.

This does, of course, increase the cost of the dish, since you’ll be buying three lobsters instead of two, but that third lobster can be a less expensive one. Instead of the heftier 1 1/2–pound lobsters for the main two whose shells will be used for serving, the third lobster can be a smaller one-pounder, and it can even be a cull (the name for a lobster missing a claw), which lowers the price even more.

Look, this isn’t an everyday kind of recipe, and it’s not an inexpensive one. If we’re gonna do it, let’s do it right.

Make a Stock for Enhanced Lobster Flavor

Just to back up for one moment, the sauce in lobster thermidor that is used to dress the meat is something like a mornay-velouté hybrid. I know I’m tossing around a lot of French cuisine jargon, so I’ll break it down: Both mornay sauce and velouté are roux-based sauces, meaning they’re thickened with a cooked paste of fat and flour. In the case of mornay, the roux thickens milk, just like béchamel, but then cheese (typically Gruyère) is melted in; another way to say that is mornay is a bèchamel sauce with cheese melted into it. Velouté is just like a bèchamel as well, except instead of milk, the liquid added to the roux is usually some kind of stock or broth; velouté doesn’t traditionally have cheese. Thermidor blends all of that together: a broth that’s thickened with a roux and finished with cheese, plus the mustard that is another defining element.

Most recipes I’ve seen for lobster thermidor offhandedly call for some kind of fumet (fish stock) or shellfish broth to make the thermidor sauce. This is a missed opportunity, and it’s where I’m cutting my own path for more lobster flavor.

Given that I’m sitting on a small mountain of lobster shells, especially from that extra lobster I’ve added for its meat, there’s no reason not to make a quick, rich lobster stock with them. It doesn’t take long: cook some shallots, garlic, and celery in oil, add the lobster shells and sear them, stir in a little tomato paste for umami depth and a richer red color, then deglaze first with brandy or sherry, then additional water. It all gets simmered for just a bit until we have a flavorful stock, then strained. At that point it’s ready for the thermidor sauce.

I can’t understate the effect this lobster stock has on the recipe. Instead of a less-focused, vaguely seafoody sauce to toss the chunks of lobster meat in, this sauce doubles down on the lobster flavor. The best way to describe it is to imagine a mayo-dressed lobster roll, but instead of mayonnaise, imagine a sauce that’s similarly creamy but warm, savory, and tasting even more deeply of lobster than the meat itself. Honestly, there’s a strong argument for making this recipe and stuffing the warmed dressed thermidor meat into a buttered and griddled split bun instead of the leftover shells. I could see lobster stock–spiked thermidor lobster rolls selling like absolute hot cakes.

Funny how I wound my way back to my preferred ways of eating lobster—now I’m dreaming of lobster rolls again. But this time, thermidor is on the menu.

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