Homemade fish stock is an essential ingredient for seafood risotto, soups and sauces. It is easy to make and handy to keep deep-frozen.
For 1 liter (1 quart) of fish stock:
1 kg (2.2 pounds) of fresh fish bones and heads of white fish (fatty fish such as salmon gives a different flavor)
450 grams (1 pound) of mixed aromatic vegetables such as carrots, leeks, celery stalks, onions, fennel trimmings
1 sprig thyme
1 bay leaf
some pepper corns
Make sure to remove the gills and eyes from the fish heads and soak the fish bones and heads in cold water to remove blood.
Clean the vegetables, but you do not need to peel the onion(s). Chop the vegetables fine, easiest in a food processor.
Sauté the vegetables in some olive oil in a big stock pot until they are fragrant and start to color somewhat.
Add the fish pieces and cover with cold water. Do not add more water than necessary, because then you end up with a watery stock.
Heat uncovered to a simmer that never breaks into a boil. Simmer for 30 minutes and skim scum from the surface.
Strain through a fine strainer. The stock is now ready to use or to freeze.
To save space in your freezer, you can decide to let the stock simmer some more (after straining) to concentrate it. Make sure that it does not break into a boil because that will reduce the flavor.
Please note that I do not advice to add salt to the stock, since you do not know yet how concentrated you are going to use it. It is better to add salt after the stock has been simmered down to the desired concentration.