This was shared with me by a Korean friend's mother. I'm writing it up here so that I don't forget it.
Soy sauce, sesame oil, crushed sesame seeds, ground onion, honey, fresh garlic, wine, milk, a teaspoon of instant coffee, and ginger juice. She didn't share the proportions--those are a closely guarded family secret. She just told me to play.
Marinate for anywhere from two hours to three days. You're supposed to use short ribs or flank steak, sliced nearly paper-thin, which you then either grill or stir-fry. Mrs. Pak's bulgolgi was melt-in-your mouth tender and was amazing with rice and kimchee.