How do I keep hollandaise warm without it splitting?

The reason hollandaise is a restaurant sauce is that restaurants make it to order or hold it in controlled conditions. At home, the gap between finishing the sauce and everyone sitting down is where it goes wrong. Too hot and it splits or scrambles; too cool and the butter starts to set and the sauce goes stiff and grainy. The working range for holding is narrower than the range for making.

Safety

Step by step

1. Finish the sauce slightly thinner than you want to serve it.It tightens as it stands. A hollandaise that is exactly right at the moment you finish it will be stiff in twenty minutes. Slacken with a teaspoon of warm water before you put it away.
2. Preheat a vacuum flask with boiling water, empty it, and pour the sauce in.This is the most reliable method available in a home kitchen. The flask holds it at an even temperature with no hot spots and no direct heat, and it does not need whisking. It will hold smooth for about an hour, sometimes longer.
3. If you have no flask, use a bowl over water with the heat off.Bring the pan of water to a bare simmer, turn the heat off entirely, and sit the bowl over it with a lid or a plate on top. The residual heat is enough for twenty to thirty minutes. Never leave the burner on under it.
4. Whisk it every few minutes if it is in a bowl.Standing still lets the sauce stratify, with the warmest, thinnest part at the base. Ten seconds of whisking redistributes it and tells you immediately whether it is starting to tighten.
5. Slacken with warm water rather than butter or cream as it thickens.A teaspoon of warm water at a time. More butter increases the oil load on an emulsion that is already under stress and is a reliable way to break it.
6. Set a limit of about two hours and discard the remainder.This is a lightly cooked egg sauce sitting at a temperature that suits bacteria. It is not worth keeping a bowl of it warm through a long brunch, and it should not be chilled and reused.

Tips

• Warm the serving jug or sauce boat as well. Pouring a held hollandaise into a cold jug drops its temperature enough to grain it.
• A wide bowl loses heat fast and skins over. Hold it in something narrow and deep with a cover.
• If it has stiffened but not split, a teaspoon of warm water and thirty seconds of whisking brings it back every time.
• Do not park it on the back of the hob near a lit ring. Radiant heat from a neighbouring burner is a common cause of a sauce that scrambles while nobody is touching it.

Alternatives

• Make it at the last minute with a blender: Blender hollandaise takes two minutes from a jug of yolks and a pan of hot butter. If you can melt the butter while the eggs poach, holding the sauce stops being a problem at all.
• Stabilise it with a starch: Whisking a teaspoon of cornflour slurry into the yolk base before the butter goes in gives a sauce that tolerates holding and gentle reheating far better. It is not classical and it is very slightly less silky, but for a brunch for eight it is the pragmatic choice.
• Mousseline: Folding lightly whipped cream into the finished sauce makes it noticeably more stable while standing, as well as lighter. It also dilutes the flavour, so season it a touch more strongly.
• Use clarified butter: A hollandaise made with clarified rather than whole melted butter contains less water and holds together better over time. Worth doing specifically when you know the sauce has to wait.

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