Demi-glace made on a gas grill

Toss the chicken wings, bony beef parts and aromatic vegetables with a little oil and brown them on the grill over moderate heat, moving them around, until golden brown all over, about 45 minutes; avoid burning, which concentrates in the reduction.

Spread tomato paste and a thin layer of flour on the bottom of a disposable aluminum tray.

Put the browned meat on top, leaving out any badly burned bits; set the tray dry on the grill a few minutes to roughly brown the tomato paste and flour.

Fill most of the way with water, leaving room for expansion, tent with foil, leave one burner on high and the others off, and keep at a gentle simmer for 24 hours or more, topping up the water; the bones should break almost effortlessly.

Strain into a big bowl and press the liquid from the solids.

Cool the liquid quickly in a sink of water and ice, stirring, then chill overnight (or freeze briefly) and scrape off the solidified fat.

Reduce on the grill by about half, until halfway to a glaze.

For a bordelaise, reduce shallots in red wine, ladle in demi-glace, season, reduce to a full glaze and finish with butter.

Freeze the rest in ice cube trays; dip in warm water to release.