1. Chop cabbage to make 4 cups. Mix 1 cup water with 1/4 cup salt (1 T table salt), sprinkle over the cabbage. Let stand for 30 minutes.
2. Mince onions.
3. Heat a pan and fry meat with 1 T soy sauce, 1 t garlic and 1 t pepper. When the meat is done, place in a large bowl and let cool. When cool, add minced onions to it.
4. When the cabbage has become soft, drain and squeeze in a sack (it will be become 3/4 cup). Mix with the meat and add 1 T of sesame salt and 1 T sesame oil. Add an egg to help the ingredients stay together.
5. Wrap the above filling in mandu skins. You can pan-fry or deep-fry. Because the meat is already cooked, fry just until the skins are cooked. To pan-fry: Heat the pan, add oil and put the mandu in. when the skin becomes light brown, add 3 T of water, cover and reduce the heat. They are done when you can no longer hear the water sizzling and the skin has become clear. You can fry further by turning them but I wouldn't because you risk ruining th shape of the mandu.
Note: I am not saying how much salt to add because the cabbage is salted. Taste the meat and if it is bland, add more salt. The mandu should be salty because frying will make it bland. Serve with a mixture of vinegar and soy sauce for dipping.