1. After thoroughly washing the fish bones, head, and skin, roughly chop the fish bones and trimmings with scissors.
Chop the onion. Cut the carrot. Slice the leek.
2. Melt some butter in a saucepan.
3. Add the vegetables to the saucepan. Sauté the fish bones, trimmings, and heads in butter, without browning.
4. Depending on the intended recipe, add white wine or Noilly. Add the white wine, pepper, salt, thyme, bay leaf, and water.
5. Bring to a gentle boil for 20 minutes and skim off any impurities.
6. Strain through a sieve without pressing at the end of cooking.
7. Reduce more or less to intensify the flavors.