Prepare the ingredients as follows:Naganegi: Slice it diagonally into ⅖-inch (1cm) pieces.Shiitake mushrooms: Remove the stems and cut the caps in half.Hakusai: Cut it into bite-sized pieces.Shungiku: Cut it into 1.6-inch (4cm) pieces.Carrot: Cut it into ⅕-inch (5mm) thick slices.Shirataki noodles: Rinse them with water and cut them in half. Toss them with sugar or salt in a colander and let them sit for 3 minutes. Then, rinse them under running water.Tofu: Cut it into bite-sized pieces. Put seasonings for sukiyaki sauce (sake, mirin, soy sauce, and sugar) in a small pot and cook over medium heat. Once the sugar has dissolved, turn off the heat. Sukiyaki sauce is ready.
Heat a large pot with beef fat over medium heat. Once the pot is coated with oil, remove the beef fat and add beef slices. Once they are lightly browned, drizzle a small amount of the sukiyaki sauce over them, then transfer to a plate. Repeat this process for all the beef slices.
Add the naganegi and shiitake mushrooms to the pot and cook until lightly browned.
Add the sukiyaki sauce and the other prepared ingredients (hakusai, shungiku, carrot, shirataki, tofu) to the pot. (If the pot cannot hold all of the ingredients or you are preparing more than 3 servings, use only half or one-third of them, including the naganegi and shiitake mushrooms.) Cover the pot and cook over medium heat.
Once it comes to a simmer, remove the lid and turn the ingredients over. Add the beef slices back in, cover the pot, and let it simmer again. After a few minutes, when the ingredients are cooked through, the dish is ready to be served.
(Optional) Crack an egg into each individual bowl and beat it for dipping.
If the pot cannot hold all of the ingredients or you are preparing more than 3 servings, cook the remaining prepared ingredients with sauce after eating the first batch (repeat steps 5 and 6).
(Optional) After finishing all the prepared ingredients, add the udon noodles to the pot. Simmer them until cooked. Then, enjoy.