Lobster and Shrimp Stock

I make this stock every time I boil lobsters. I save shrimp shells in the freezer when I cook shrimp (do not keep for too long, and smell them before using them as they can go bad in there), and use them to augment the stock.
When you boil lobsters, save the shells and the water used to boil them.
In a hot pan, with a little oil, 'toast' the lobster and shrimp shells (try to add the shrimp shells as dry as you can) until all of the shrimp shells change color. Add mirepoix (rough chopped celery, carrots and onions) and sauté (cook over medium-high heat) until softened. Add some tomato paste, and sauté until rust-colored. Add the water in which you boiled your lobsters - enough to just cover the shells. Bring it slowly to a simmer. Simmer 45 minutes. Strain through your finest strainer and/or cheesecloth.
Lobster stock is great in seafood risottos, stews and soups. It can be made with all lobster shells or all shrimp shells (which would obviously be a shrimp stock; this will be milder in flavor). If no lobster cooking water is available, use water. When used, your stock will need to be seasoned. Taste as you go...