If you’re discouraged seeing how much of your shellfish such as langoustines goes to waste—everything except the tail—you may want to use these parts to make “Crustacean Butter”. You can also use lobster tails, shrimp heads, or crawfish tails for the same result (use about 3 lbs of shells per 1 lb of butter as shown below).
“Crustacean butter is the classic final addition to a bisque. Also, you can use crustacean butter to saute a chicken or a piece of veal that’s destined to be topped with the crustacean in question (an example is poulet aux écrevisses/chicken with crawfish – something I used to serve in my restaurant).
When confronted with an expensive shellfish such as lobster, crayfish, oysters, langoustines, scallops, etc – consider serving the shellfish as a topping for chicken. As odd as this may sound, it actually has a long history in 18th century French cuisine. Some of it persists. Crawfish served over chicken is a specialty of Lyon. The idea is to create an interchange between the chicken and the shellfish such that the shellfish’s flavor is extended and a small amount of shellfish manages to serve the maximum number of people. What I usually do to serve the shellfish in question, is gently cook the chicken in crustacean butter (unless using oysters or mussels etc.) such that the chicken browns, but the butter doesn’t burn. When the chicken (I usually cut the chicken into 10 pieces) is ready, I keep it warm and make the sauce in the saute pan. If there’s liquid in the pan–I mean aqueous liquid, not the melted crustacean butter/chicken fat combo that’s floating on top–I boil it down until the juices caramelize on the bottom of the pan. When this happens, I pour off the fat and discard it. I deglaze the pan with a little liquid such as white wine, boil it down to a tablespoon or two, add cream and the liquid that by now will have been released by the waiting chicken.
At this point the sky’s the limit. Barely cooked pieces of crustaceans such as those mentioned can be gently reheated in the sauce, oysters can be poached in the sauce for half a second. In any case, this all leads to finishing the sauce with a little bit of crustacean butter (Cognac is also marvelous with crustaceans).” ~ James Peterson