Unless you purchased a cut of steak that is already extremely tender, you are going to need to tenderize them before you start cooking them.
To do this, lay the steaks on a cutting board, and tap it with a meat tenderizer or the backside of a knife.
It should only take about six to eight pounds with a meat tenderizer to get the steak ready.
When the meat has been flattened enough, generously season both sides of the meat with salt and black pepper.
Next. start preparing the pan by heating two tablespoons of butter into it.
I prefer to use a cast-iron skillet, but use any skillet that you have available to you in your kitchen.
Add the onions and the garlic to the skillet and sauté them for about eight minutes.
When the onions become caramelized, increase the heat to medium and pour in the mirin and the soy sauce.
Cook the mixture for about a minute so that you can reduce the amount of liquid in it by a little bit.
Add the vinegar, and then stir it for about 30 seconds longer before transferring it to a bowl.
Set the bowl aside.
Add the remaining tablespoon of butter and vegetable oil to a large skillet.
You can use the same one if you'd like.
Once the butter has melted, cook the steaks over medium-high heat.
Cook the steak for about four to five minutes.
This will give you a medium-rare steak, but you can cook it longer if you prefer your steak well done.
Flip the steaks once during the cooking process.
Once the steaks are cooked, you will want them to rest before you cut them.
I like to allow the steaks to rest for about three to four minutes.
While the steaks are resting, put the onions back into the skillet and allow them to cook for 30 seconds to a minute.
This allows the onions to take on some of the flavors from the steak, which will make it even tastier when you enjoy it.
To serve garnish the steak with onions and parsley.