Sauce Diable — the devil's sauce — is the most aggressive of the espagnole derivatives, a reduction-driven preparation where white wine and vinegar are concentrated with shallots until nearly dry, then rebuilt with demi-glace and finished with a sting of cayenne pepper that should make the diner sit up without making them suffer. The technique is a masterclass in controlled reduction: shallots in fine brunoise are sweated in butter, then white wine and white wine vinegar (in equal parts) are added and reduced to a near-glaze — perhaps two tablespoons of sticky, intensely acidic liquid. This reduction is the flavour engine. Demi-glace is added and the sauce simmers for 15 minutes, then is strained through a chinois, pressing the shallots. Cayenne pepper is added off heat — a pinch at a time, tasting between additions. The heat should be perceptible but not painful: a slow warmth that builds on the back of the palate. Freshly ground white pepper is added alongside for complexity. The finished sauce should be dark, glossy, sharply acidic, and warm with chilli heat. It is the traditional sauce for grilled spatchcocked chicken (poulet à la diable), where the bird is pressed flat, brushed with mustard and breadcrumbs, grilled, and served with the sauce on the side. The sauce also pairs well with grilled chops and devilled kidneys. The devil is in the balance — too much cayenne kills the palate, too little and the sauce is merely an acidic brown sauce without character.
Reduce wine and vinegar to near-glaze — this is the flavour concentrate. Cayenne added off heat, pinch by pinch, tasting constantly. Heat should build slowly on the back palate — not assault the front. Strain for smooth finish. Acidity forward — this is an aggressive sauce by design.
For a more complex heat, replace half the cayenne with piment d'Espelette — the Basque pepper adds a fruitier, slower-building warmth. Add a teaspoon of Worcestershire sauce with the demi-glace for additional fermented depth. If serving with devilled kidneys, stir a tablespoon of the kidney's cooking butter into the finished sauce for richness that bridges the protein and the sauce.
Under-reducing the wine-vinegar base — the sauce tastes thin and one-dimensional. Adding cayenne to the boiling sauce — makes it impossible to control the heat level. Using hot sauce or chilli flakes instead of cayenne — different flavour profile and heat distribution. Making the sauce too hot — it should challenge, not punish.
Escoffier, Le Guide Culinaire; Larousse Gastronomique