First, we need to melt the butter. This needs to be done five minutes or so ahead of time so that the milk solids can sink to the bottom. This is important for when we whisk in the butter as it allows us to control the consistency of the sauce.
Place a large pot filled to a third with water on to boil. Choose a stainless steel mixing bowl that sits on top of the pot but does not touch the water and place the egg yolks, lemon juice, zest and vinegar into the mixing bowl.
Turn the heat down to just under a simmer, this is the ideal heat and won't cook the yolks too fast.
Sit the bowl over the water and gently whisk the yolk mixture in the bowl over the water and they will slowly start to heat and increase in volume. Don't forget the purpose of the whisking is not to aerate the mixture so much as to avoid the yolks catching and also ensuring even thickening.
You will notice the yolk mixture becomes a little thicker on the bottom and around the edges. Keep a towel around the outside of the bowl so that you can remove it from the heat if it starts to form lumps from heating to fast.
Keep the yolk mixture moving constantly by whisking continuously. You will notice the bubbles that form will get smaller and smaller and soon become the larger part of the yolk mix as the runny yolk cooks.
The only thing that is important to remember at this stage is that if it starts to catch, lift the bowl above the pot to slow down the heating.
In around five to ten minutes, the yolk mixture should be holding it's shape like a soft whipped cream and the texture should be as smooth. This means the yolks are cooked but not to the point of being scrambled and you have made yourself what is called in French cooking a "sabayon".
Next comes the whisking in of the butter, make sure the butter is boiling hot. Place the sabayon bowl onto a damp cloth so it won't spin while you whisk.
While whisking fast slowly pour on the butter keeping a steady stream of butter but keep the stream as thin as possible.
Don't add more butter than you can whisk in, if the sabayon is overloaded it will split the mixture (be patient especially if you are a beginner).
At first, the whisking is quite easy but as the butter is slowly incorporated, it becomes a little tougher. Add the butter slower at this stage to compensate.
As you near the milk solids, be at your most diligent not to add too much as the hollandaise is more likely to split at this stage, then slowly pour in the milk solids while still whisking, this will loosen the hollandaise and set the consistency.
Usually adding all the milk solids is the correct amount of moisture that the hollandaise needs, but it can be too much so add slowly in case you don't want the hollandaise to be that thin.
Alternatively, if you have added all the milk solids and it is still thicker than you would like, add a little boiling water to compensate.
Variation can occur due to the size of the eggs. Check the seasoning, transfer to a small stainless steel bowl and cover with cling film.
Keep in a warm place until serving time. You can make the hollandaise up to two hours safely before you need it.
If the butter has been added too fast and has split slightly, you can use a blender to blitz the emulsion and save it. Please remember to keep the sauce warm, if it cools too much the butter will start to set and you guessed it "split", the most dreaded of all kitchen terms to a chef.