Lobster Thermidor: Expensive? Yes. A myriad of pricey ingredients? Yes. Time consuming? Yes. Worth it all? Absolutely.

I began my experimenting with Julia Child’s wonderful recipe, but then started adding my own personal touches, ingredients, and methods. If you want to impress guests with  an elegant, elaborate and exquisitely delicious dinner, Lobster Thermidor is a great bet. For an interesting history on how Lobster Thermidor may have been inspired by a French play, click here.

To view another of my lobster recipes—Lobster in Champagne Sauce with Green Grapes—click here.

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You’ll need at least two live lobsters at 2 to 2 1/4 pounds each so that you have shells large enough to be filled. Mine cost me nearly $100. I’m quite certain I’ve never seen the dish offered on a restaurant menu. I’m sure this is because they would need to charge a fortune for it. And that again is what makes Lobster Thermidor a very special dinner. The nice part about making Lobster Thermidor is it all can be prepared a day ahead of time, refrigerated, then baked just before serving.

It’s not really difficult to make, but requires many steps and a lot of time. I give a very detailed breakdown of the process below.

Begin by making a fumet or seafood stock. Cut the onion, carrot, and celery stalk in thin slices. In a very large kettle, simmer the wine, vegetables, bay leaf, sprigs of parsley, thyme, and tarragon, peppercorns, and salt for at least 15 minutes.

Turn up the heat and bring the mixture to a rolling boil. Add the live lobsters, cover the kettle, and boil for about 15 minutes, until the lobsters are bright red and the long feelers can be pulled out rather easily.

Remove the lobsters from the kettle, and immediately plunge them in ice water to stop the cooking.

When they have cooled, split them in half with a sharp, heavy knife beginning at the top of the head and ending at the tip of the tail.

With a spoon, scoop out the grayish-green tomalley and the red roe, should there be any, and set aside.

I used to discard this disgusting looking green slime until I discovered that it’s pleasantly delicious and adds greatly to the sauce.

Carefully remove the meat from the tails and set aside. Detach the claws, then remove the meat and add it to the tail meat. Carefully wash and dry the half shells, making certain you don’t break them.

Force the tomalley and/or roe through a fine sieve and set aside.

Slice the mushrooms, and stew them slowly in a heavy covered pan with 2 tablespoons of butter, 1 tablespoon lemon juice, and 1⁄4 teaspoon of salt for about 10 minutes.

Strain out the mushroom liquid and set it aside, saving the mushrooms for later.

Strain the lobster cooking juices, pressing down on the vegetables and herbs to extract as much flavor as possible. You should have between 2 1⁄2 -2 3⁄4 cups of juice.

Add the mushroom liquid to the lobster liquid in a saucepan and boil down to concentrate the flavors until reduced to about 1 2⁄3 to 2 cups.

Add the 3⁄4 cup of milk, and keep the liquid at a simmer.

Mince the two shallots. In another saucepan, melt 5 tablespoons of butter, then add the minced shallots, and cook gently for about 2 minutes.

Whisk in the flour and cook for another 2-3 minutes.

Add the simmering lobster-mushroom-milk liquid, whisking until the sauce is very thick.

In a large bowl, beat the egg yolks, then beat in 1⁄2 cup of heavy cream, the tablespoon of dry mustard, the sieved tomalley, and 2 generous pinches of cayenne.

By droplets, beat the hot lobster sauce into the egg yolk, cream mixture.

Then return the mixture to the saucepan, bring it to a boil, and boil slowly for a couple minutes. Add about a tablespoon or more of fresh lemon juice to taste. Whisk in 1⁄2 cup of the grated Gruyère cheese, and continue to whisk and cook until the cheese is melted and well combined in the sauce. Other cheeses, such as Parmigiano or Swiss Cheese, are sometimes substituted, but Gruyère is traditional and the best choice.

At this point check the sauce for seasoning and thickness. It should be thick enough to coat a spoon quite thickly, yet not be pasty. If it is too thick, add enough extra cream or milk, until you get a nice consistency. Film the top of the sauce with 1 tablespoon or so of heavy cream to prevent a skin from forming, and set it aside.

Chop the lobster meat and cut it into small cubes. In a large skillet, melt 4 tablespoons of butter over moderate heat. Add the lobster cubes, and sauté, stirring slowly for about 5 minutes until the lobster turn a rosy color.

Add 2 tablespoons of the chopped tarragon and the cognac, and continue stirring until the liquid is reduced by half.

Fold the mushrooms and two-thirds of the sauce into into the lobster meat, along with the tablespoon of Madeira or Sherry. Taste for salt and pepper.

Place a rack in the upper third of the oven and preheat it to 425°. Place the empty lobster shells in a large, shallow roasting pan.

Carefully spoon the lobster mixture into the shells, heaping it as high as possible without having it spill over. Carefully spread the remainder of the sauce over the lobster, then sprinkle the remaining 1⁄2 cup of grated cheese on top.

Place in the oven for about 10 minutes or so, until the lobster is beginning to bubble. If the top has not yet browned, run the lobsters under a broiler for a couple minutes, until nicely browned.

Sprinkle the remaining chopped tarragon over the lobsters, and serve on large plates with lemon wedges.

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