To make the teriyaki glaze mix together the soy, sake, mirin and sugar and stir to dissolve the sugar. If the sugar will not dissolve, heat the glaze in the microwave for 10-20 seconds, or in a small saucepan on the stove, and stir again.
Heat a heavy frypan over medium heat and add the oil. Fry the garlic until lightly browned, then remove and drain on absorbent paper. Increase the pan heat to medium-high and add the steaks, browning well on all sides.
Add the glaze to the pan around the steaks and repeatedly flip the steaks through the glaze, cook the steaks to your liking and checking doneness by pressing the steak with your fingers. As the glaze begins to thicken it will stick to the steaks. Remove the steaks to a warm plate in a draught-free spot, pour over any sticky glaze left in the pan, and rest for 5 minutes.
Slice the steaks, arrange the slices on a plate and scatter over the garlic.
For the buttered greens, but the gai lan into 8cm lengths and quarter the pak choy. Bring a large pot of water to the boil and add butter. Then add the thicker stems of the gai lan to the water first, then the thinner stems, bok choy, and finally the spinach. Add the salt and mix well. Remove the vegetables and strain.
Serve the steak with the buttered vegetables and steamed rice.
Suggested other greens – Broccoli, Broccolini, Bok Choy