Cut the beef into bite-sized pieces.
Slice the onion thinly.
Heat oil in a pan and stir-fry the beef.
When the beef is halfway cooked, add the onions and stir-fry together.
Make a sauce with soy sauce, sugar, and cooking wine, then add it to the pan.
Put the sautéed beef and onions on top of rice.
For extra flavor, top with egg yolk and green onions as desired.