First make the garlic chips. Heat the oil in a small frying pan, add the thinly sliced garlic and fry gently over a low heat for about 5-6 minutes.
Once the garlic begins to colour, remove and drain on kitchen paper. Be careful not to cook until golden as they will continue to cook after draining.
Soak the thinly sliced onion and radish in salted water for 10-15 minutes. Then rinse well and squeeze the water out completely.
Heat a frying pan until hot. Brush the beef with oil (use your hands!)
Cook the oiled meat in the hot pan until browned all over. It is important to seal the beef all over, including the ends, first and then continue cooking to desired level.
Once the beef is cooked to the level you wish, remove from the pan and marinade in a mixture of soy sauce and mirin, which will be re-used for the sesame sauce later. Make sure all the juices from the pan go into the soy sauce mixture as well.
Set the beef aside for at least 30 minutes. This makes it easier to slice and also allows it to absorb flavours from the sauce.
To make the sesame sauce, remove the beef from the soy and mirin sauce (and set aside). Add the tahini paste, sugar and water and mix well. (Reiko warned us that the sauce may split initially but if you keep mixing, it will re-combine into a smooth creamy sauce).
Slice the beef about 5mm thick.
To plate the dish, first create mounds of onion and radish and lay a slice of beef over each.
Generously spoon some sesame sauce over each slice of beef.
To finish, garnish with a sprinkle of garlic chips.
