Start with the sauce. Brown the remains/shells in olive oil. Chop garlic and vegetables, and add them to the pan with the tomato purée. Fry for 1 minute. Pour the cognac over. If surroundings allow, ignite the cognac. If not, ­reduce the cognac and let it evaporate entirely. Pour
the white wine over, let it boil for 1 minute, then add the cream. Let the pot simmer gently for 1 hour. Drain through a sieve, and discard everything but the liquids. Season to taste with salt and pepper. Add the roe and smooth the sauce with a hand blender before serving.

Prise the shell halves apart. Cut the white muscle away from the shell. Cut each muscle into 4 pieces. Season with salt and pepper, then quickly fry on all sides in a frying pan.