Terrines:
In a food processor, combine the shelled langoustines, softened butter, Brandy, and beaten egg.
Mix until a homogeneous consistency is achieved.
Pour in the cream in a thin stream and mix for 30 seconds.
Season with salt and pepper.
In 4 small buttered ramekins with a diameter of 2 and 1/2 inches (6 cm) and a height of 1 and 1/2 inches (4 cm), add a circle of parchment paper to the bottom so that the terrines do not stick.
Fill the ramekins with the terrine mixture and place them in a shallow dish.
Add boiling water to the dish until it reaches one quarter of the height of the ramekins.
Bake in the oven for 30 minutes.
Let the terrines rest at room temperature for 45 minutes before serving.
Langoustine Sauce:
In a saucepan, heat the oil and quickly sear the langoustine shells until they are colored.
Add all the remaining ingredients (except the cream).
Cover and bake in a preheated oven at 450 F (230 C) for 30 minutes.
Strain the shell pieces, mash them, and return them to the sauce.
Cook over high heat, whisking constantly, and reduce the sauce.
Strain the mixture through a fine-mesh sieve, then add a little cream.
Refrigerate until ready to use.
Serve the terrines on a bed of langoustine sauce.