Step 1: Marinate the Beef : In a bowl, combine sliced beef with soy sauce, sesame oil, and black pepper. Mix well and set aside to marinate for 10–15 minutes while you prepare the broth.
Step 2: Prepare the Broth : In a large pot, heat sesame oil and vegetable oil over medium heat. Add garlic and ginger, and sauté for about 30 seconds until fragrant. Pour in beef broth, soy sauce, oyster sauce, rice vinegar, and mirin. Bring to a gentle simmer and let the flavors meld for about 10–15 minutes. Adjust seasoning with salt, pepper, or more soy sauce if needed.
Step 3: Cook the Beef and Vegetables : Add the marinated beef slices to the simmering broth. Cook for 3–4 minutes, or until the beef is tender and cooked through. Add mushrooms, bok choy, and carrots, and simmer for another 3–5 minutes until vegetables are just tender.
Step 4: Cook the Ramen Noodles : In a separate pot, bring water to a boil. Add ramen noodles and cook according to package directions (usually 3–4 minutes). Drain and rinse lightly to prevent sticking.
Step 5: Assemble the Bowls : Divide the cooked noodles evenly into serving bowls. Ladle the hot beef and vegetable broth over the noodles. Top each bowl with green onions, a soft-boiled egg (if using), and a sprinkle of sesame seeds.