How to make it
For Marinade: Heat soy sauce, sesame oil, mirin, lime juice and sake in a pan and bring to a gentle simmer. Take off the heat and stir in spring onion and garlic. Set aside to cool.
For Beef: Season beef with salt and pepper and let sit at room temperature for 10 mins. Heat sesame oil in a frying pan on high heat and sear beef for one minute on each side. Let sit on a chopping board for 5 mins then pop in a large ziplock bag with marinade for at least an hour (overnight is best).
Remove beef from marinade, roll in sesame & hemp seeds, then slice as thinly as possible with a sharp knife.
To assemble: Drizzle the tostada shell with japanese mayo, top with a slice of tomato, beef tataki, micro radish and an extra sprinkle of seeds and marinade!