In a bowl, mix soy sauce, gochujang, sesame oil, brown sugar, minced garlic, and ground black pepper. Add the beef and let it marinate for at least 30 minutes (or overnight if you have time).
In another small bowl, combine mayonnaise, sriracha (or Korean chili sauce), sesame oil, garlic powder, and an optional pinch of sugar. Mix until smooth and set aside in the fridge until ready to use.
In a pot over medium heat, bring your chicken or beef broth to a simmer. Stir in gochugaru, soy sauce, rice vinegar, sesame oil, and salt. Once it's bubbling away beautifully, add in your ramen noodles and cook them until al dente (about three minutes).
Heat a grill pan or skillet over high heat. Sear the marinated beef for about two to three minutes on each side until it's nicely caramelized. Let it rest briefly before slicing against the grain.
In serving bowls, add your ramen noodles topped with hot broth. Drizzle on that creamy sauce generously before adding slices of grilled beef. Finish off with chopped green onions and toasted black sesame seeds.