Mince half an onion
Add the minced onion and the hamburger into a large bowl
Add 1.5 tsp soy sauce, 4 tbsp of panko, salt, pepper and an egg to the bowl
Mix everything by hand
After mixing, divide the hamburger into 4 even batches to make 4 patties
Form the patties into an oval shape, slap against your hands to remove the air, and gentle press the center in the top to evenly cook the meat
Melt the butter on a fry pan and add the hamburger patties. Fry over medium heat for about 2 minutes. Flip the hamburger and fry again for about 2 minutes
Flip the hamburgers every 2 minutes until their form solidifies. After solidifying, cover pan with a lid and cook on low heat for 5 minutes
After finishing the hamburger, remove the patties, but keep the remaining oil as a base for the sauce
Add the mushrooms and fry them on medium heat in the left over oil
Add the ketchup, the Worcestershire sauce, and 1.5 tsp of soy sauce.
Simmer the sauce and the mushrooms on low heat for 5 minutes
Add the sauce to the hamburger patties and enjoy!