As far as the dressing goes, I?m a fan of the classic but I don't add the egg yolk here. The flavor of the anchovy, even if you just use a little oil that the anchovies are packed in, becomes more important if you omit the egg. I make the dressing in advance and keep it in the door of the fridge but then I mix it with the lettuce at the very last second. If your dressing doesn't come together, whisking in a splash of warm water can often help!