Gather all the ingredients.
Dice onions. In a medium sized fry pan, add 1/2 tbsp butter on medium heat. Once butter is melted, add onion, cook until browned and set aside. Should take around 2-3 minutes.
Grate garlic with a grinder or a garlic press. Put into a large mixing bowl.
In the mixing bowl, add ground pork, ground beef, salt, pepper, egg, half & half, nutmeg, panko, cooked onions from step 2). Combine with hands until mixed well.
Take 1/4 of the mix and throw from one hand to another while gently cupping the mix with the palm and hand forming a ball. Place the ball onto a plate and press down on it with the palm of your hand to form a patty. The patty should be around 1 inch thick. Afterwards, take your thumb and gently press and make an indent in the middle of the hamburger patty. This ensures the hamburger will retain its shape during the cooking process (otherwise it will expand upwards). Repeat until all the mix is used up.
Fill 1 mixing bowl with flour, 1 mixing bowl with beaten eggs, 1 mixing bowl with panko.
Take a patty and dip in the following order: flour > eggs > panko. Once coated, place into air fryer tray and air fry for 13-16 minutes at 360F or until internal temp reaches 165F.
In a small mixing bowl, combine ketchup, Worcestershire Sauce, Oyster Sauce and sweetener. Mix well and set aside.
Once menchi katsu are air fried, transfer to serving plate and enjoy with tonkatsu sauce from step 9).