Begin by marinating the thinly sliced beef in soy sauce, sake, grated garlic, and grated ginger.
Next, prepare the sauce by mixing together oyster sauce, sake, and black pepper in a bowl.
Heat a frying pan over medium-high heat and add vegetable oil along with the broccoli florets.
Stir-fry the broccoli until it is well coated with oil.
Add the marinated beef to the pan and stir-fry until it is nearly cooked through.
Incorporate the cooked udon noodles and the prepared sauce into the pan.
Continue to stir-fry until the noodles are heated through and the sauce has been absorbed.
Serve the dish immediately on plates.
