1. Put the onion, salt, pepper, white vinegar and white wine into a pan and reduce until there is only 2 tbsp of liquid remaining. At this point, remove the pan from heat and allow to cool.
2. Meanwhile, melt the butter on the stovetop or in a microwave.
3. Select a saucepan and metal bowl, the bowl needs to fit on the saucepan (creating a Bain Marie). Fill the saucepan with an inch or so of water, and bring to the boil. *
4. While waiting for the water to boil, add the egg yolks and 2 tbsp of the reduced liquid into the metal bowl (discard the onion) and whisk to combine.
5. Once the water has started to boil remove the pan from the heat, place the metal bowl containing the egg mixture onto the pan (making sure the bowl doesn’t touch the water) and begin to whisk. The best way to whisk is in figure of eights; this gets all the mixture moving and therefore helps to avoid the egg mixture cooking!
6. Continue whisking until the mix starts to thicken, this happens when the egg gets above 80˚C. At this point remove the bowl from the pan but continue whisking as heat will still be being transferred from the bowl to the mix. It is very important that the mix thickens, but does not over cook. **
7. Whilst continually whisking, start to add the melted butter a few drops at a time. The hollandaise should thicken as you add the butter. The thicker it becomes the faster you can add the butter, but patience is definitely required for this step. You will see the butter has separated and the bottom layer is now made up of milk solids. Stop when you get to this layer and discard these.
If in step 7 the hollandaise is not thickening try add a tsp of hot water and whisk vigorously. This often thickens the hollandaise.
* bowl selection can be critical to this recipe, I recommend a thin metal bowl as this heats up and cools down quickly, giving you more control over temperature of the egg.
** If the egg mix is not heated sufficiently the egg will not thicken and the butter will not combine in step 7. If the egg is over heated the egg will start to cook and you will end up with lumpy hollandaise