3 lb Rinsed shrimp heads & shells
4 qt Water

You may also use crawfish heads and/or shells, or rinsed fish carcasses
(heads and gills removed), or some combination.

In a large stockpot, combine the watere and the seafood. Bring to a boil.
Reduce the heat, cover, and simmer 3 to 4 hours, or until the liquid is
reduced by half. Remove from the heat and strain through a sieve. Allow it
to cool slightly, then refrigerate or freeze in batches until needed.

note: I generally throw in some coarsely chopped onion, bell pepper and
celery to add some additional flavor. But if you just want the seafood
taste, which is needed for some of the delicate sauces, just use this basic
recipe.