Place the very thin slices of flank steak between two sheets of plastic wrap or parchment paper and pound each one into uniform thinness
Trim the root off of the green onions and lay two over each portion of pounded beef
Roll the beef up tightly like a cigar and secure with several toothpicks (optional)
Lightly dust each roll with rice flour and shake off the excess (optional)
Place a large skillet over medium heat and add a tablespoon of a neutral oil
Brown the rolls starting with the seam side for about 3 minutes per side or until the outside is crisp and the inside is about medium rare (about 9 minutes total)
Transfer the beef rolls onto a plate, remove the toothpicks, if used, and set aside
Add 2 cloves of finely minced garlic, 1 teaspoon of grated ginger, 1/2 cup soy sauce, 1/4 cup of mirin, 2 tablespoons of granulated sugar and 1 tablespoon of toasted sesame oil into the skillet and bring to a simmer
Once the sauce thickens, add the beef rolls into the skillet and spoon the sauce over the rolls
To serve, slice the rolls into bite sized pieces and garnish with white sesame seeds and thinly sliced green onions
Serve over rice or noodles (optional)