1. In a medium bowl, combine soy sauce, mirin, sake (if using), brown sugar, grated ginger, minced garlic, toasted sesame oil, and black pepper. Whisk until the sugar dissolves and the marinade is well mixed.
2. Add the thinly sliced beef to the marinade, making sure each piece is well coated. Cover the bowl and let it marinate in the fridge for at least 30 minutes, or up to 2 hours for deeper flavor. I often do this step in the morning before the chaos begins.
3. Heat a large skillet or grill pan over medium-high heat. No need to add oil—the sesame oil in the marinade does the trick.
4. Once the pan is hot, add the beef slices in a single layer, working in batches if necessary to avoid overcrowding. Cook for about 1-2 minutes per side, or until nicely browned and just cooked through. Watch closely—thin slices cook fast!
5. Remove the beef from the pan and transfer to a serving dish. If you like, pour any remaining marinade into the pan and simmer for a minute to thicken slightly, then drizzle over the beef for extra flavor.
6. Garnish with sliced green onions and toasted sesame seeds before serving.

One trick I’ve learned over the years is to marinate the beef ahead of time—sometimes even overnight—so the flavors really sink in. Also, don’t overcrowd your pan; it’s tempting to throw it all in at once when you’re juggling dinner and kids, but giving the beef space helps it caramelize better. I know firsthand how messy counters and a crowded stove can get, but a little patience here makes all the difference.