Chef John from Food Wishes just posted a new video about making lump-free bechamel sauces and he says, "Hot roux, cold milk, no lumps." This reminded me of the conflicting information out there about how to get a lump-free bechamel sauce. I've heard the hot roux, cold milk combo, and I myself use the hot roux, hot milk combo (as advocated by Julia Child). And I think I've also heard about every hot-hot, cold-hot combo there is. Why all the differences? And what combo will guarantee that you DO get lumps?