This was absolutely delicious except way, way too much salt! And I only did 3/4 of a tsp total. 1 tsp must be an error. Next time I'm not going to put any salt in until the very end and I'll do it just to taste. When the sauce was ready I just covered it and put it on the back burner with no heat and had no issues with it curdling. It was not very hot when I poured it on the plate, but I was ok with that. I put this over croissant toast and I highly recommend it.
BTW, I think the best way to keep hollandaise is in a thermos. When I was a working chef, I would keep my hollandaise in a pre-warmed thermos and it would keep throughout breakfast service (2-3 hours). Trying to keep it in usable condition on a warm flame is probably doomed to fail, unless a water bath is used, and that is iffy, IMHO.
The recipe for the hollandaise sauce was easy to follow and while it was labor intensive, the sauce turned out excellent. The part folks should be VERY weary of is how to keep the sauce warm while you finish the recipe. I followed resting instructions precisely as I assembled the toast and egg, only to come back and find my beautiful hollandaise curdled and browned. It was on the lowest heat setting possible for my stove, so the only way I could have avoided it was by letting the sauce rest without any added heat at all. It was infuriating to see that beautiful sauce destroyed because of such a simple, easy-to-avoid step.
I fixed my curdled hollandaise by whisking boiling water into it drop by drop and switching to an electric whisk. I may still have to whisk another egg yolk in if it doesn't keep well overnight.
Suggestion to publisher: do a test-kitchen run through before posting intricate sauce recipes to ensure that it can be replicated by home cooks that may have varying levels of heat available to them. It was very surprising that the recipe offered a solution to curdling at the start of the recipe, but not for curdling that results in the resting process.
The only reason I didn't rate this recipe lower is because the food was very tasty once the sauce was fixed. However, it shouldn't take 2 hours to make brunch because you end up spending extra time finding piece-meal solutions.