Take 450 g beef roasting joint and stab it all over with a fork. Sprinkle it with salt and pepper all over, and rest to room temperature (approx 30 minutes, less in summer).
Heat a frying pan on medium with ½ tbsp cooking oil. Once hot, place the beef in the pan and sear on each side until lightly browned and a thin crust has formed.
Add 2 cloves garlic, 3 slices ginger root, 1 Japanese leek (naganegi) (green part, save the white part for later), 120 ml dashi stock, 4 tbsp Japanese soy sauce (koikuchi shoyu), 4 tbsp sake, 1 tsp light brown sugar, and 4 tbsp mirin to the pan. Bring the mixture to a boil.
Once boiling, lower the heat to simmer and cover with a lid. Simmer for 10 minutes, turning the meat over halfway through.
Remove the beef from the pan and wrap it tightly with foil. Leave the beef and marinade to cool to room temperature.
Once cooled, unwrap the beef and discard the foil. Remove the garlic, ginger and leek from the sauce and discard. Place the beef in a sealable bag and pour in the sauce. Marinate in the refrigerator for at least 6 hours, preferably overnight.
Take the meat out of the bag and pour the leftover marinade into a pan. Finely dice the leftover white part of the leek, and add it to the sauce. Bring to a boil and let it bubble for 2-3 minutes or until slightly reduced and thickened.
Turn off the heat and add 4 tbsp grated daikon radish (daikon oroshi). Mix well and serve hot or cold according to your preference.
Cut the beef into thin slices, a similar thickness to deli meats if you can.
Arrange the slices on serving plates and top with the sauce, a sprinkle of finely chopped green onions and a small blob of wasabi. Enjoy!
Notes
If you're worried about doneness, use an instant-read thermometer and stop the gentle simmer around medium-rare. The meat will continue to cook slightly as it rests and chills.Chill the beef thoroughly before slicing, then cut very thinly.If the sauce tastes too strong after reducing, loosen it with a splash of water or dashi before adding the grated daikon. Its natural juices will further mellow the saltiness.Store sliced beef in an airtight container for up to 3 days with the sauce kept separate, avoid freezing.Serving ideas:Traditional miso soup, Spinach ohitashi, Hiyayakko (chilled tofu with toppings), Simmered kabocha squash