To make the Teriyaki sauce, combine all ingredients in a saucepan. Stir the mixture well. Put it on medium heat and bring to a boil. Turn the heat down to low and simmer for a couple minutes. Stop the heat and cool the mixture.
Heat a griddle pan until really hot and almost smoking. Rub the steaks with the oil, salt and pepper. Griddle the steaks for 2 minutes on each side so that they’re medium rare. Leave to rest. While the beef is resting rub the British asparagus with a little oil then lay on the griddle and grill for 2-3 minutes, turning every now and then until they start to soften but still have `bite’ and have little chars on them.
Split the asparagus between two plates. Carve the steaks into 1cm strips and lay on top of the Asparagus pouring over the meat juices left from resting. Cover each steak with a few tablespoons of Teriyaki sauce and sprinkle with sesame seeds.