but the traditional and most popular way is to use thinly sliced beef. How thin, you ask? No more than a quarter inch thick. But this isn't just a stylistic choice or a culinary tradition.
Chill until ready to serve alongside the beef. Carve the beef into thin slices just before serving. Both the beef and the sauce can be prepared up to two days in advance. If you want to get ahead ...
Buy well-marbled beef labelled for yakiniku, not the type for shabu-shabu, which is sliced too thin. If you want to be really extravagant, use wagyu beef. An optional ingredient is wasabi - but ...