I made some Korean Mandu a few weeks ago. One thing that I love about Korean food is that they used very little oil and they're healthy. I guess, that's why Korean are so slim! I got the recipe from Maangchi. Head over her website and watch the video to learn how to fold and make that ripple shape (Mine doesn't look as good as hers).
In Maangchi recipe, these mandu is pan fried with some oil and covered. My mom deep fried them instead. I think, deep frying them makes the skin a bit tough.
One thing that I love about these mandu is that you can put them in your freezer and fry them later :) It's very convenient, don't you think?