A compound brown sauce of caramelised onions deglazed with white wine and white wine vinegar, enriched with demi-glace. Sauce lyonnaise takes its name from Lyon and shares its defining ingredient (slowly caramelised onion) with the city's most celebrated preparations. It is the classical sauce for preparations à la lyonnaise — calf's liver (Entry 94), poached eggs à la lyonnaise, grilled meats. The distinction between sauce lyonnaise and onion soup is the quantity of liquid: the sauce has a concentrated nappe; the soup is a broth.
- Onions: very finely sliced, caramelised in butter for 20–25 minutes until deep gold and sweet. - Deglaze with white wine (100ml) and white wine vinegar (50ml) — the vinegar is characteristic and must not be omitted. - Reduce by two-thirds. - Add demi-glace. Simmer 10 minutes. - Strain through a fine sieve, pressing the onions. - Mount with cold butter. - The finished sauce should show no onion pieces — it is a smooth, deeply flavoured sauce that communicates the caramelised onion entirely through aroma and flavour.
Jacques Pépin's Complete Techniques