Tip the miso paste, Sherry or sake,
sugar and garlic into a sealable food bag.
Season with a generous grinding of black
pepper, then squash it all together until
completely mixed. Add the steak, gently
massage the marinade into the steak
until completely coated, then seal the
bag. Pop the bag into the fridge and leave
for at least 1 hr, but up to 2 days is fine.