• Gather all the ingredients.
  
• Cut 1 tomato in half and remove the stem end. Slice into wedges, then cut them in half crosswise.
  
• Slice 1 green onion/scallion into thin rounds and set aside.
  
• Beat 1 large egg (50 g each w/o shell) in a small bowl.
  

To Cook

• Add 2 cups chicken stock/broth to a small pot or saucepan. Add 1 tsp soy sauce and 1 tsp toasted sesame oil and stir to combine. Cover the pot and bring it to a boil over medium heat.
  
• Add 1 oz dried vermicelli (bean threads) to the boiling broth. Once the noodles begin to soften, separate them with cooking chopsticks. Cover the pot and bring it to a simmer. Nami's Tip: The vermicelli will cook in 2–3 minutes (follow your package instructions), so add the tomatoes and egg at the right time so the noodles don't overcook.
  
• Once it's simmering, add the tomatoes. Season with ⅛ tsp white pepper powder. Taste the soup and add ⅛ tsp Diamond Crystal kosher salt, to taste; you may not need it if your chicken stock/broth is already salted. Warm the tomatoes and bring the soup back to a gentle boil.
  
• When it's boiling gently, slowly pour a thin stream of beaten egg into the soup in a spiral pattern; avoid drizzling on top of egg that you already poured. For better control, I place my cooking chopsticks at the bowl's edge and let the egg drizzle down into the soup. Let the egg sit for 15–20 seconds until they become fluffy ribbons. Turn off the heat to prevent overcooking.
  

To Serve

• Sprinkle with sliced green onions and ladle into individual bowls. Serve at the table with optional la-yu (Japanese chili oil). and additional sliced green onions on the side.
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for up to 2 days.