In a large bowl or Ziploc bag combine the soy sauce, brown sugar, mirin, sesame oil, beer, garlic, and black pepper.
Add the steak, cover (or seal the Ziploc bag) and refrigerate for 8 to 24 hours.
Remove from marinade, sprinkle with salt, allow to sit at room temperate for 15 minutes.
Grill (preferred method):
Preheat the grill to medium-high. Grill until seared well on both sides, about 4 minutes per side.
Remove, allow to rest for 5 minutes. Slice against the grain, sprinkle with sesame seeds and green onions.
Oven:
Preheat the oven to 350.
Heat cooking oil in a cast iron skillet until very hot. Add the steak, cooking until well seared, about 2 minutes. Flip, cook for two minutes on the other side. Add to the oven and cook for 4 minutes for medium rare.
Notes
*Mirin is a sweet Japanese cooking wine that is often found in the Asian section of the market. If you can’t find it, dissolve ¼ teaspoon sugar in 2 tablespoon white wine or sherry.