Mince the onion and microwave for 30 seconds at 600W. Coat the boiled quail eggs with flour.

Mix breadcrumbs and milk in a bowl. Add ground pork, onion, salt, and pepper, then mix until sticky. Divide into 8 portions and wrap each around a quail egg, shaping into balls.

Heat salad oil in a pan over medium heat. Add the meatballs and cook until browned, turning frequently. Cover and cook on low heat for 2-3 minutes until fully cooked, then remove.

Using the same pan, add butter, ketchup, and tonkatsu sauce. Heat on low while stirring until the sauce thickens.