1. Marinate the Beef (Optional):

   • In a bowl, combine the sliced beef, soy sauce, sake, and cornstarch. Mix well and let it marinate for about 10 minutes to enhance flavor and tenderness.

2. Prepare the Broth:

   • In a large saucepan, combine the dashi (or beef broth), soy sauce, mirin, sugar, and salt. Bring to a gentle simmer over medium heat.

3. Cook the Udon Noodles:

   • If using dried udon noodles, bring a large pot of water to a boil. Add the noodles and cook according to package instructions, usually about 8-10 minutes. Fresh udon noodles will only need about 2-3 minutes.
   • Once cooked, drain the noodles and rinse under cold water to remove excess starch.

4. Stir-Fry the Beef:

   • In a large skillet or wok, heat a tablespoon of oil over medium-high heat. Add the marinated beef (discard any excess marinade) and stir-fry for 2-3 minutes, or until browned. Remove the beef from the skillet and set aside.

5. Cook the Vegetables:

   • In the same skillet, add a little more oil if needed. Add the shiitake mushrooms, carrots, and bok choy (or spinach). Stir-fry for about 3-4 minutes until the vegetables are tender.

6. Combine Ingredients:

   • Return the cooked beef to the skillet with the vegetables. Pour in the simmering broth and allow everything to cook together for an additional 2-3 minutes, allowing the flavors to meld.

7. Assemble the Dish:

   • Divide the cooked udon noodles among serving bowls. Ladle the beef and vegetable mixture along with the broth over the noodles.

8. Garnish and Serve:

   • Top each bowl with chopped green onions and any additional toppings you desire, such as nori, sesame seeds, or a soft-boiled egg. Serve immediately and enjoy!

Tips:

• You can customize the vegetables based on your preference or seasonal availability. Bell peppers, snap peas, and broccoli are great alternatives.
• For a spicy kick, consider adding some chili paste or shichimi togarashi to the broth.
• This dish can also be made vegetarian by substituting the beef with tofu and using vegetable broth.