Rub the beef with sake and a pinch of salt and pepper.

Cut the broccoli into small florets and trim the root of the shimeji mushrooms, separating them by hand.

Mix the sauce ingredients (sake, soy sauce, mustard, salt, and pepper) in a bowl.

Place the broccoli and 1 tbsp of water in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 1 minute. Drain the water.

Heat salad oil in a frying pan over medium heat, add the beef and grated garlic, and stir-fry until the beef changes color.

Add the shimeji mushrooms and stir-fry until softened, then add the broccoli and stir-fry together.