Freeze the steak for 30 minutes. Toast the sesame seeds in a dry pan over medium heat for 3 to 4
minutes, shaking the pan gently, until the seeds are golden brown. Remove from the pan at once to prevent burning. Crush the seeds in a food mill or with a mortar and pestle. Slice the steak into thin strips, cutting across the natural grain
of the meat. Combine the steak, soy sauce, garlic, spring onions and half the
sesame seeds, mixing well. Marinate for 2 hours. Combine the oils and brush them onto a cast-iron grill-plate,
heavy-based frying pan or barbecue plate. Heat to very hot and cook the meat in 3 batches, searing each side
for about 1 minute (don't overcook the steak or it will become chewy). Re-brush the grill with oil and allow it to reheat to very hot
between batches. Sprinkle the extra crushed sesame seeds over the steak and serve
with Kim Chi.