01 - Rinse the 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 to 3 minutes until softened.
03 - In a bowl, combine dashi stock, soy sauce, mirin, sake, and sugar. Pour into the skillet with onions and bring to a gentle simmer.
04 - Add sliced beef evenly into the skillet. Simmer for 5 to 7 minutes until beef is cooked through and tender, skimming off any foam or fat as needed.
05 - Fluff the cooked rice and divide it among serving bowls. Spoon the beef and onion mixture along with some sauce over the rice.
06 - Top with sliced spring onions and pickled ginger if desired. Serve immediately.