I learned to make this bisque from a top classically trained French chef. In his preparation, the stock was simmered for a few hours and then the shells were beaten/pulverized with a heavy metal spoon in a china cap with the stock poured over regularly and then the stock was passed through a very fine chinois several times and then it was reduced before adding the heavy cream. Other than the technique, the secret is adding a bottle of sauternes to the stock.
While I have a china cap and chinois just for this bisque, I'll probably just pull the shells out and sieve a few times.
My sense is shrimp shells have so little substance, a stock would take next to no time. There's a lot of meat in these lobster shells making this closer to veal stock in time and preparation.
It is, by far, the best lobster bisque I've ever had.
Starting to reduce it a little now, will strain and sieve and let it sit overnight and finish for tomorrow night's dinner with a small lobster.
