Have a look at the little 'Unai's first day - behind the scenes' video.

[Sir C]

So you simply put the hot butter in in lieu of oil and did the smooshy smooshy thing and it worked?

That's me eating Eggs Benedict and steak bearnaise every day now. : prayforburney:

Yep. 2 egg yolks, some lemon juice and mustard and seasoning, gave that a momentary blitz, then poured the melted butter in. It just hollandaised, instantly. I popped it in a thermos and it held perfectly for half an hour.