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, 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. Allow it to cool to room temperature. Remove the garlic, ginger and leek, and discard. Save the sauce for later.
Once cooled, unwrap the beef and discard the foil. Place the beef in a sealable bag and add the leftover sauce. Marinate in the refrigerator for at least 6 hours, preferably overnight.
Once marinated, 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 even slices.
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!