I like hollandaise sauce on eggs Benedict. To make that sauce, I usually use the packet of dry powder from the grocery store, but, lately, I’ve tried to make it from scratch (with the encouragement of my wife).
Most of the online recipes make it using a blender: add egg yolks and lemon juice to a blender, then slowly drip in melted butter. I did that, but the results were not as good as I’d hoped, so on Saturday I tried the old fashioned method: very slowly warm the yolks, lemon juice, and butter with continuous mixing. This produced a somewhat thick, yellow hollandaise sauce. On pouring it onto warm toast, ham and a warm egg, the sauce fell apart: the butter melted and separated from the uncooked egg yolks.
Ah, the chemistry is that the egg yolks have to coagulate (“denature”, if you’ve taken biochemistry), and that requires heat. On Sunday I made the sauce again, but this time I heated it up more (a heat setting of 3 out of 9) and mixed it continuously for 10-15 minutes. Eventually, the sauce got thick. It was warm enough to feel quite warm to the touch. On pouring it over the eggs, this time the sauce stayed thick.
My wife says that, to use the blender method, the butter has to be really, really hot. That might work. The blender has a lot of glass in it, so I’m not sure the butter would provide enough heat to warm the yolks up. Have to try that some other time!