It's an emulsion made with egg yolks and fat, and finished with vinegar. So, basically warm mayonnaise, right?
Never made hollandaise before, but wanted to try this amazing looking technique.
Took a long time, but it just worked. Whisked for 15 minutes, but started on water that was probably not warm enough. I halved the recipe, so used 2 egg yolks, 55g butter, and 40ml of hot water. Cooked it until the bottom of the bowl stayed visible for a moment as I moved the whisk through it. Added salt, pepper and balsamic vinegar. Will need to have supper to use it up!
Ignore the poaching technique,it might work if your eggs are very fresh, but it didn't work at all for me.
Lytham