1 lb thinly sliced beef ribeye, brisket, or sirloin
1 tablespoon vegetable oil or other neutral oil
1 cup thinly sliced onion
6 oz tofu, cubed (the firmness of your choice; I prefer extra-firm)
½ cup shredded mozzarella cheese (optional)
¼ cup mung bean sprouts, blanched and drained (optional)
¼ cup thinly sliced scallions
1 tablespoon sesame seeds
The night before or 1-2 hours ahead: Whisk together the soy sauce, mirin, sake, brown sugar, garlic, ginger, and crushed red pepper. Combine with the beef in a large Ziploc bag or shallow covered dish and let marinate for 1-2 hours, or ideally overnight.
The day of: Prepare an oven-safe dish. Heat the vegetable oil in a large skillet over medium heat until shimmering. Add half the beef in a single layer to the pan, along with half the marinade, half the tofu and half the onions. Let cook, stirring, until beef is cooked through and onions are softened, about 4-5 minutes. Taste and adjust with more soy sauce and brown sugar, if desired. Remove to the oven-safe dish and repeat with the remaining beef, tofu, and onions. Sprinkle the cheese over top (if using) and slide the dish under the broiler for 5-10 seconds, just until the cheese is melted. Add the mung bean sprouts, scallions, and sesame seeds. Enjoy with warm rice.