The mother of every serious brown sauce.
Brown roux, brown stock, mirepoix, tomato. Reduce with an equal quantity of veal stock and you have demi-glace — the depth-charge behind steak au poivre, chasseur, bordelaise.
Cook 60g flour in 60g butter over medium heat until deep chestnut, stirring — 15 minutes.
Add 200g finely diced mirepoix (onion, carrot, celery), sweat 5 minutes, then a tablespoon of tomato purée.
Whisk in 1L warm brown veal stock. Simmer 90 minutes, skimming religiously.
For demi-glace: strain, then reduce this by half against a further litre of veal stock. Total time — half a day.