Thinly slice the flank steak against the grain into bite-sized pieces. In a small bowl, whisk together the soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, and black pepper for the marinade.

Add the sliced beef to the marinade, toss to coat, and let it marinate at room temperature for at least 15 minutes while you prepare other ingredients, or refrigerate for up to 4 hours.

Prepare your eggs as desired: soft-boil for 6-7 minutes, then immediately transfer to an ice bath before peeling and halving, or fry them sunny-side up.

Chop the scallions, roughly chop the bok choy, and slice the shiitake mushrooms. Set aside.

Heat a skillet over medium-high heat. Once hot, add the marinated beef in a single layer (cook in batches if necessary to avoid overcrowding) and sear for 2-3 minutes per side until browned. Remove the beef from the skillet and set aside.

In a large pot, heat 1 tablespoon of sesame oil over medium heat. Add the minced garlic and grated ginger and sauté for about 1 minute until fragrant.

Stir in the gochujang and gochugaru (if using) and cook for another minute, stirring constantly, to bloom the flavors.

Pour in the beef broth, scraping up any browned bits from the bottom of the pot. Whisk in the soy sauce, rice vinegar, and sugar. Bring the broth to a simmer, then reduce heat and let it gently simmer for 5-7 minutes to allow the flavors to meld.

Add the sliced shiitake mushrooms and bok choy to the simmering broth and cook for 2-3 minutes until the bok choy is slightly wilted but still has a bite.

While the broth simmers, cook the instant ramen noodles in a separate pot of boiling water according to package directions (usually 2-3 minutes). Drain well.

Divide the cooked ramen noodles into two serving bowls. Ladle the hot broth with mushrooms and bok choy over the noodles.

Arrange the seared beef slices, halved eggs, chopped scallions, crumbled roasted seaweed, and a sprinkle of toasted sesame seeds on top of each bowl. Serve immediately and enjoy!