Combine soy sauce, sugar, garlic, ginger and 12 cups water in saucepan and simmer until sugar dissolves. Cool. Stir-fry 6 ounces steak per serving in 1 tablespoon oil until brown. Add 1/4 cup soy sauce mixture and 2 scallions and bring to a simmer. Add 1 teaspoon cornstarch mixed with 1 teaspoon cold water and simmer until sauce thickens.