Hollandaise

Set a heatproof bowl over a pan of barely simmering water — the bowl must not touch the water, and the water must steam, not boil. Add the yolks and the water (or vinegar reduction). Whisk constantly and vigorously, lifting the bowl off the heat every few seconds to control the temperature, until the yolks triple in volume and thicken to a pale, airy sabayon that holds a ribbon. This is the make-or-break stage: too much heat scrambles the yolks into sweet curds; too little and they never thicken enough to carry the butter.

Off the heat (or with the bowl resting on a damp towel for stability), begin adding the warm clarified butter in a thin, steady stream while whisking without pause. Start drop by drop until the emulsion takes and visibly thickens, then increase to a slow trickle. The butter must be warm, not hot — around 40-50 C / 105-120 F — and the sabayon warm too, so the fat stays fluid and droplets disperse evenly. Add butter faster than the yolks can absorb it, or let either component get cold, and the emulsion breaks into an oily, separated mess.

Whisk in the lemon juice a few drops at a time, tasting as you go — it brightens the sauce and loosens it slightly. Season with salt and a small pinch of cayenne. The lemon should lift and balance the richness without making the sauce taste sour; the cayenne is a background warmth you sense more than taste.

Hollandaise is a live, fragile emulsion that cannot be reheated. Hold it warm — not hot — in its bowl set over (not in) warm water around 50-60 C / 120-140 F, or in a warm spot near the stove, whisking occasionally. Use within an hour or two. Above roughly 65 C / 150 F the yolks scramble and the sauce breaks; let it go cold and the butter sets and separates.