Perfect Hollandaise every time using a blender/food processor? I was a cook at a cafe recently that was buying in Hollandaise. I started making the sauce from scratch following the same basic procedure each time but got varying results. sometimes the Hollandaise would be too thick; more like a butter spread than a sauce. Then, for a real long stretch right up til I got my current office gig, the stuff wouldn't thicken at all and just stayed runny.

This is the procedure i followed every time:


Melt half a pound of butter in the microwave
Carefully separate 2 eggs
Add egg yolks to blender and blend until aerated
Add capful of white vinegar
Add pinch of salt
Slowly add melted butter


What changes should I make to this procedure so my Hollandaise will come out perfect every time? What factors were likely for causing the failed (too thick or not thick at all) batches? And how does the temperature of the liquid butter factor in?

No offense intended to any food purists, but I'm not interested in answers that feature whisks and/or double boilers. Answers featuring blenders/food processors only please. Thank you!
I have used the exact same procedure that you describe on a number of occasions, and the result has always been a thick butter-like consistency, and I think that this is pretty much unavoidable when using a food processor. Maybe you can get a thinner consistency if you use the whole egg like ElendilTheTall suggested. 

Anyway, since the sauce never emulsified, I think you have been pouring in your butter too quickly. It is important to just add a few drops at a time until the sauce has started emulsifying. After that you can go faster, but it should still only be a thin stream. 

Also, something that I have noticed is that when using a food processor with only a small amount of egg yolks (or any ingredient, for that matter) is that the rotating knives will actually rotate above the ingredients and not actually mix them. When making hollandaise/mayonnaise, that will be fatal since you will just be pouring butter on top of a thin layer of egg yolks. So you might want to check your food processor and see if it works similar to mine. 

While I realise that you use this recipe because it is easier than making hollandaise by hand in a bain-marie, I would suggest that you at least try making it "for real" once before settling on this method. The consistency is so much nicer. I think the flavour is better too but that may only be my imagination.