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