Simple and very rich! These deliciously soft and creamy potatoes are worth the splurge on any special occasion. This dish is full of cream, and there's no acceptable substitute. For a gratin to make your guests say, "Wow!, I have to have more," and make you think, "Oh no, I hope they don't eat the whole thingI want some for breakfast," you need real cream, and lots of it. Originally from my paternal (Polish) grandma, this version of potato gratin contains no cheese which, she said, "would compete with the delicate flavor of the leeks."