I originally made this to satisfy my best friend's cravings for beef bulgogi, but it's turned into our ultimate comfort food, especially with homemade kimchi. There are two versions, depending on how much time you have. —angiecita
To make the marinade: In a medium bowl, combine soy sauce, vinegar, sesame oil, mirin (if using), 1 T brown sugar, garlic, jalapenos (or Sriracha) , and half the green onions. Taste the marinade and make sure it is primarily sweet and salty, and that you can taste the smokiness of the sesame oil. Add more soy sauce and/or sugar to achieve a well-balanced marinade.
Two ways to prepare the beef:
If you have the time, place the steak in a ziploc bag, add the marinade, and set the bag in the fridge to marinate overnight, or up to 24 hours.
Heat peanut oil in a grill pan on high. Add the steak and cook 2 minutes on each side. Lower heat to medium-high, and continue cooking steak 8 minutes more on each side. Remove steak from pan and place on cutting board. Tent loosely with aluminum foil and let sit 10 minutes, then slice steak across the grain as thinly as possible.
If you are running short on time, place the steak in the freezer for 15 minutes, then slice across the grain as thinly as possible. Place the steak and marinade in a ziploc bag or large tupperware container. Place in fridge to marinate 1-2 hours, shaking the container occasionally.
Heat the peanut oil in a large skillet on medium-high, add the beef and a few tablespoons of marinade. Saute steak 4-8 minutes, depending on desired doneness.
Scoop rice into bowls, top with steak, green onions, and sesame seeds. Add kimchi, Sriracha, and other condiments as desired.