Take the beef out of the refrigerator and bring it to room temperature. Sprinkle both sides with salt and pepper just before cooking.

Mince the onion and thinly slice the garlic, removing the core.

Heat garlic and salad oil in a frying pan over low heat until the garlic turns golden brown. Remove the garlic and set aside. Increase to medium heat and add the beef, cooking for 2 minutes on each side.

Remove the beef and wrap it in aluminum foil. Let it rest for about 5 minutes.

In the same pan, sauté the minced onion over low heat for 3–4 minutes until lightly browned and translucent. Add the sauce ingredients (sake, mirin, soy sauce) and simmer while stirring.