1. Prepare Marinade and Slice Steak:

• Gather all your ingredients. Chop the green onions and mince the garlic.
• In a large glass or ceramic bowl, whisk together the soy sauce, chopped green onion, white sugar, minced garlic, toasted sesame seeds, toasted sesame oil, and ground black pepper until the sugar is mostly dissolved and the marinade is well combined.
• Prepare the flank steak: For easiest slicing, you can partially freeze the flank steak for about 30-60 minutes until it’s very firm but not frozen solid. Using a very sharp knife, slice the flank steak against the grain into very thin strips (aim for 1/8-inch thickness or less).

2. Marinate the Steak:

• Add the thinly sliced flank steak to the bowl containing the marinade.
• Toss the steak slices thoroughly with the marinade using your hands or tongs to ensure every piece is evenly coated.
• Cover the bowl with plastic wrap and place it in the refrigerator. Let the beef marinate for at least 1 hour. For deeper flavor, you can marinate it for up to 4 hours or even overnight (though for very thinly sliced beef, a few hours is often plenty).

3. Preheat Grill:

• When ready to cook, preheat your outdoor grill (or indoor grill pan/heavy skillet) to high heat.
• Lightly oil the grill grates to prevent the marinated steak from sticking.

4. Grill the Bulgogi:

• Remove the marinated flank steak slices from the refrigerator.
• Working in batches to avoid overcrowding the grill (which would lower the temperature and cause the meat to steam rather than sear), quickly place the steak slices in a single layer on the preheated, oiled grill grates.
• Grill for just 1 to 2 minutes per side. Because the steak is sliced so thinly, it cooks incredibly fast! You’re looking for it to be slightly charred in spots and cooked through.
• Use tongs to flip the slices and cook the other side.
• Remove the cooked Bulgogi from the grill as each batch is done and transfer to a serving platter.

5. Serve:

• Serve the Grilled Beef Bulgogi immediately while hot and sizzling!
• Garnish with extra chopped green onions or toasted sesame seeds, if desired.
• Enjoy this flavorful Korean BBQ treat!