Mince garlic and ginger root. Slice mushrooms thinly. Cut asparagus diagonally. Set aside.
Cut sliced beef into 2" width pieces. Put beef in a bowl, season with 1/2 Tbsp Sake, salt, and potato starch and mix.
Heat 1/2 Tbsp oil in a wok, and cook beef until slightly browned. Remove meat to a plate, and set aside for a moment.
In the same wok, add 1/2 Tbsp oil, garlic, and ginger, and cook for a minute. Add mushroom and asparagus, and stir-fry until vegetables are just cooked through. Move beef back to the wok. Season with 1 Tbsp Sake, soy sauce, and oyster sauce. Stir and serve.