Two closely related compound brown sauces that form a family with sauce lyonnaise — all sharing the foundation of a wine-and-vinegar-based reduction with demi-glace. Sauce Robert: white wine and onion reduction with demi-glace, finished with Dijon mustard added off heat. Sauce charcutière: sauce Robert with the addition of fine-cut cornichons, making it the canonical sauce of the charcutier's table — served with grilled pork, sausage, and pied de cochon. Both require the mustard added off heat (the same principle as sauce gribiche and rognons) — heated mustard loses its volatile isothiocyanates and the sharp note that defines both sauces.
**Sauce Robert:** - White wine + finely chopped onion, reduced to nearly dry. - Add demi-glace. Simmer 10 minutes. - Strain. - Off heat: Dijon mustard, 1 tablespoon per 200ml sauce. - Mount with cold butter. **Sauce charcutière:** - Sauce Robert as above. - Add fine julienne of cornichons — blanched briefly if you prefer their sharpness moderated, raw if you prefer the contrast. - Do not strain after adding cornichons. Decisive moment: Adding the mustard off heat, every time, without exception. Mustard heated above 70°C loses the allyl isothiocyanate compounds that give Dijon its characteristic punch. Once these compounds are driven off by heat, no additional mustard can restore them — the sauce becomes mild and round rather than sharp and clean.
Jacques Pépin's Complete Techniques