Source: I imagined that this was a “traditional” recipe with well-defined ingredients / steps, but as I searched every single recipe had something different, so I can’t pinpoint any specific. So the source is something inside http://www.bing.com/search?q=lobster+thermidor+recipe.
History: According to Wikipedia, the traditional “Lobster Thermidor” was created in the end of the 19th century by a Parisian restaurant in honor of the eponymous play (which, unlike the recipe, didn’t get much success). I remember my father making this (with shrimp, if I recall correctly) recipe when I was a kid and I loved it. And a few weeks back when I found at my local Costco a bag of langoustine tails, and decided to use the famous recipe of its larger cousin.
Variation from the original: As I mentioned, I can’t tell exactly which one is the “real” original. Some recipes asked for shallots, other onions (I used onions); some asked for cognac, other for wine (I went with cognac); some went with egg yolks, some without (I didn’t use them); most asked for raw lobster (I had a bag of cooked langoustines), and so on.
Ingredients from specialty stores: I don’t remember finding langoustine before, so I think this is a specialty ingredient, but I found it at Costco (not really a specialty store) – and lobster (or even shrimp) could be used for this recipe.
- 2 lb. cooked langoustine tails, thawed
- 3 tbsp. butter
- 1 tbsp. olive oil
- 1/2 cup cognac
- salt & pepper
- 1 medium onion, finely diced
- 5 tbsp. butter
- 5 tbsp. flour
- 1 tsp. ground mustard
- 1/2 cup heavy cream
- 1/2 cup milk
- salt & pepper
- gruyere cheese for gratin, about 1/2 cup grated
In one large saucepan, add the butter and when it melts, add the onion and cook until it’s soft, with some salt and pepper. Add the flour and the mustard, mixing well. This can be done ahead of time.
In another pan, heat the butter and the olive oil, and add the langoustines seasoned with salt and pepper, cooking for just 3-5 minutes (they’re already cooked). As the langoustines start losing liquid, remove it with a ladle and move to the other pan. When it’s almost dry, add the cognac on fire and flambé until the fire is extinguished (if there is still too much liquid in the pan it won’t be long). Place the langoustines in an oven-proof, deep dish.
Back to the sauce pan, add the milk and the cream, mixing well. When it’s well combined, add the sauce on top of the langoustines, and grate gruyere cheese on top to cover. Bake in a 350ºF (175ºC) oven for about 15 minutes, until the cheese is golden brown (or use a broiler which can make it faster).