1 small Yellow onion, sliced in half from top to bottom, then sliced paper thin into semi-circles, soaked in ice water for 30 minutes, drain very well
3Scallions, chopped (For special touch, cut themwhere the white bottoms branch off into green tops. These highly prized parts of the scallion are called hành trần. Split them into 1½-inch (3.8 cm.) pieces and cook them with the noodles)
2tbsp. Roughly chopped cilantro (leaves and stems)
Wrap raw beef in plastic; chill in freezer for 30 minutes or until semi-firm. Slice as thin as possible (⅙ of an inch 0.1 cm. is ideal). If meat begins to defrost while slicing, place back in freezer until firm. (Meat sliced this way is routinely available at Asian markets.)
Soak the rice noodles in warm (80° to 90°F or 27° to 32°C) water until softened, about 30 minutes; drain and set aside.
Slice the beef that was cooked in the broth into slivers, about 1/8 inch (0.3cm.) thick.