To make the teriyaki sauce, combine the brown sugar, mirin, sake and soy sauce in a small bowl and stir to combine.

If your steak is very lean, rub a teaspoon of oil onto each steak. If the steaks have a lot of fat marbled in with the meat they shouldn't need any oil. Heat a heavy bottomed frying pan over high heat until very hot. Add the the steaks and sear one side until browned.

Flip the steaks over and sear the other side. If you want your steaks medium rare, reduce the searing time, if want your steaks well done, increase the searing time.

If you have oil pooling in your pan, drain the excess oil. Pour the teriyaki sauce into the pan with the beef, and let it boil.

Flip the steaks over repeatedly until the teriyaki sauce is very viscous and coats each steak in a thick shiny glaze. Transfer the steaks to a cutting board and let them rest for a few minutes.

Slice your beef teriyaki with a sharp knife. Drizzle the remaining teriyaki sauce onto the sliced steaks and serve.