White Sauce: Combine all ingredients together and taste: add more hot sauce if you'd like. This gets better as it sits and can be done a few days in advance as part of your meal prep!
Steak: Heat a large cast iron skillet over medium high heat for at least 5 minutes with a drizzle of oil - it should be very hot but not smoking. Sprinkle the steak cubes (1 inch or slightly less) all over with salt and pepper.
When the skillet is very hot, add the steak in one layer and let cook undisturbed for 1-2 minutes until very brown on the first side. Flip the steak around a few times to brown on most sides, cooking quickly to avoid overcooking the steak.
After about 4 minutes (more or less, this depends on the thickness of your steak and how hot your pan is), add the soy sauce, butter, and lemon juice to the pan. Toss everything together and turn the heat off.
Serve with rice, white sauce, and/or hibachi vegetables. Enjoy!