Rich chicken jus (chicken demi-glace)

Put the chicken carcasses in a pot; for speed, break them into smaller pieces with a cheap knife or cleaver.

Add onion (peeled for a clearer stock), celery and carrot, and black peppercorns.

Cover with water by an inch or two so the chicken stays submerged as it reduces.

Bring up over high heat until just barely simmering, then turn down to hold a bare simmer with a few lazy bubbles.

Skim the scum and fat as it rises, early and as it goes, for a clearer, more concentrated stock.

Simmer about two hours, skimming occasionally.

Taste only with a pinch of salt added, since the unsalted stock tastes bland; strain into a pot through a strainer and discard the solids.

Reduce the three quarts of stock over very low heat at a gentle simmer for a few hours, to keep the aromatics and avoid burning.

When reduced to about a quarter, strain through a fine mesh strainer into a clean smaller pan.

Keep reducing, carefully skimming the protein skin that forms without taking much liquid.

Near the end, check every few minutes so it does not burn; stop when thick and the bubbles are large and viscous. No salt is needed.

Scrape into a container; it sets firm when cooled. Reheat in the microwave rather than on the stove to avoid burning or over-reducing.