Beurre Blanc - cold/warm - salted/unsalted ?

[mrip541]

When making beurre blanc do you use cold or warm butter, and do you use salted or unsalted butter? Why one over the other? Until yesterday I thought you used cold unsalted butter but just heard Bourdain tell us to use warm salted butter. What's the deal?

[pikawicca]

I use cold, unsalted.