Place 2.5 cups (~625ml) of water into a pot. Drop in 2-3 Kelp pieces, a small handful of Katsuobushi Flakes, and 1 Shiitake Mushroom. Place it on a high heat and bring it to boil.
Once the pot is boil, pick out the shiitake mushroom and set it aside for later (we'll use it as a topping). Then grab a strainer and scoop out the flakes & and kelp from the broth.
Now, season the broth with 2 Tablespoons of Hontsuyu Sauce.
Followed by a small amount of Soy Sauce (1 teaspoon!)
Next, blanche the thin cuts of shabu shabu into the broth - just until the beef pieces lose their red. Take the pieces out and set aside for later.
Once the pot comes to a boil, you'll see residual foam gather on the surface. Scoop this out with a soup ladle for a clean-tasting broth.
Then place your udon noodles into the broth. Let the noodles boil away for 2 minutes.
(While you wait, cut the boiled Shiitake Mushroom into thin slices)
If you want to include a poached egg: After 1.5 minutes into the Udon noodles cooking, crack-in an egg. Cover the pot with a lid and let it boil away for 30 seconds.
Now turn off the heat. Carefully garnish with Sliced Shiitake Mushroom, green onions, mungbean sprouts and Shabu Shabu Beef. If you like - sprinkle on a touch of the Shichimi Spice Mixture (or Korean Gochugaru).