Sprinkle all sides of the 460 grams beef chuck flap with the ¼ teaspoon salt and let it come up to room temperature for about 30 minutes.
460 grams beef chuck flap, ¼ teaspoon salt
To make the tangy wasabi cream sauce, mix the ¼ cup Japanese mayonnaise, 2 teaspoons lemon juice, and 2 teaspoons wasabi in a small bowl. Cover and refrigerate.
¼ cup Japanese mayonnaise, 2 teaspoons lemon juice, 2 teaspoons wasabi
When the beef is ready, use paper towels to wipe off any liquid on the surface. If your beef is lean, you'll need to rub a generous coating of oil on the meat.
Heat a frying pan over medium heat until it's hot but not scorching. Place the beef in the pan and let it brown on one side, undisturbed.
Roll the beef onto the next side and let it brown before repeating until all 4 long sides of the beef are browned. Check the side of the beef; it should be cooked about ¼ of the way through on every side.
Use a paper towel to soak up any excess oil in the pan, and then add ¼ cup water and quickly cover the pan with a lid. Turn down the heat to low and steam for 8-12 minutes or until the beef reaches 120°F (49°C).
¼ cup water
Flip the roast beef over once halfway through steaming.
When the meat has hit 120°F (or 130°C if you want medium rare), remove it from the pan and let it rest for at least 10 minutes.
To make the onion sauce, add the 70 grams onion to the pan you roasted the beef in. Turn up the heat to medium and sauté them until they're golden brown (~4 minutes). If your beef is lean, you may need to add some oil to the pan.
70 grams onion
When the onions are golden brown, deglaze the pan with the ¼ cup sake.
¼ cup sake
When the mixture no longer smells like alcohol, add the ¼ cup soy sauce and 2 tablespoons evaporated cane sugar. Boil the mixture until it starts to thicken.
¼ cup soy sauce, 2 tablespoons evaporated cane sugar
Once the roast beef is done resting, use a sharp knife to slice it as thinly as possible.
To assemble the roast beef don, split the 1 batch cooked short-grain rice between 3 large bowls and mound it up. Drizzle some onion sauce onto the rice.
1 batch cooked short-grain rice
Layer the roast beef around the rice and make an indentation in the center.
Drizzle the onion sauce on the beef, then sprinkle with freshly cracked black pepper and chopped 2 scallions.
2 scallions, black pepper
Drizzle some of the wasabi cream sauce on one side of the rice bowl, and then top each donburi with an egg yolk from 3 large eggs.
3 large eggs