Leave the steak out at room temperature for 30 minutes to 1 hour.
Very thinly slice green onions. Peel and slice garlic. Set aside.
Season the steak with salt and pepper. Heat oil in a frying pan over medium heat, then add sliced garlic. Cook until the garlic is browned and crispy, then remove it from the pan. In the same pan, cook the steak for 3-4 minutes on each side, searing around the edges as well. To check if the steak is cooked to your liking, measure the internal temperature. It should reach at least 125°F (52°C)for medium rare doneness. Remove the meat from the pan, immediately wrap with aluminum foil, and let rest for 5-10 minutes.
In the same pan, add sake, soy sauce, and butter. Cook until it’s just about to boil, then remove from heat.
Slice the beef into 1/4" (6 mm) thick pieces, plate, and drizzle with the sauce. Top with green onions and garlic chips.