Lightly season the beef with salt and pepper. Shred the maitake mushrooms apart into easy-to-eat pieces.
Heat some oil in a frying pan, spread out the beef slices and cook quickly until it's still a bit red. Move aside to a plate.
Put the frying pan on medium heat, melt the butter in it and add the mushrooms. Stir fry.
When the mushrooms are cooked, return the beef to the frying pan and stir-fry quickly.
Add some coarsely ground black pepper, swirl in some soy sauce and it's done.
Story Behind this Recipe
When I was a newlywed, I bought some shabu-shabu beef at a neighborhood supermarket, and stir-fried it with maitake mushrooms in butter, and my husband loved it. It's delicious without having to use expensive meat!
Shabu-shabu beef cooks up the tenderest. If you cook it too long it will become tough, so stir fry briefly with the maitake mushrooms. You don't need to use expensive beef. Very thinly sliced shabu-shabu beef is fine.