Followed step by step Nigella's Hollandaise recipe and it was perfect until I squeezed in the lemon juice. The juice of the first half was fine but I added a squeeze more which made the sauce split and runny. Why?
Nigella's Hollandaise sauce recipe (in HOW TO EAT) is a classic version of the sauce, made by whisking egg yolks and butter together over a low heat. Hollandaise usually splits if the sauce becomes too hot or gets too cold. The recipe uses a bowl set over a saucepan of simmering water as this reduces the risk of the sauce becoming overheated. However, if the sauce looks like it is splitting during cooking then you can dip the bowl into a pan of cold water and whisk quickly to cool the mixture down.
We wonder if the lemon was fridge cold. If it was then the addition of cold lemon juice could have just been enough to cause the sauce to split by becoming too cool. You may be able to rescue the sauce by whisking in a teaspoon or two of warm water (a few drops at a time) to help to warm it again and re-emulsify the sauce. Otherwise you could put an egg yolk into a clean bowl, put this over the saucepan of hot water and then whisk in the split hollandaise a little at a time, which should help to give a smooth sauce again. If you make hollandaise again then try to use a room temperature lemon and we suggest adding the lemon juice a little at a time and tasting in between additions, to make sure that the sauce doesn't become too acidic.