1Finely dice the Onion. In a pan, sauté the diced Onion over medium heat with a small amount of Vegetable oil until softened and translucent, about 5-7 minutes. Let it cool completely.
2In a large bowl, combine the Ground pork, Ground beef, cooled sautéed Onion, half of the Egg (lightly beaten), Koikuchi soy sauce, Mirin, Salt, and Black pepper. Mix thoroughly by hand until well combined and slightly sticky.