We go to Greece as often as possible and I love Tzatziki, I more or less live on it whilst there. This is the most authentic recipe that I've ever come across, unfortunately in the UK people seem to think that you put mint in it but I've never had it that way whilst in Greece. This is taken directly from a cookbook I picked up whilst in Crete, its by Margaret Phoca called The Best Greek Dishes. The only alteration I make is I tend to reduce the oil to 2 or 3 tbsp just to make it more healthy and I use Greek Extra Virgin Olive Oil. Cooking time is chilling time.