01 - Rinse rice under cold water until clear. Combine rice with water in a rice cooker or saucepan and cook following manufacturer or package instructions.
02 - Heat vegetable oil in a large skillet over medium heat. Add sliced onions and cook for 2 to 3 minutes until softened.
03 - In a bowl, whisk together dashi stock, soy sauce, mirin, sake, and sugar. Pour mixture into the skillet with onions and bring to a gentle simmer.
04 - Add beef slices evenly into the pan. Simmer for 5 to 7 minutes until beef is cooked through and tender. Skim off any foam or excess fat as needed.
05 - Fluff cooked rice and divide into serving bowls. Spoon beef and onion mixture with sauce over rice. Garnish with spring onions and pickled ginger if desired. Serve immediately.