Prep the veggies: Finely dice the tomatoes to small bite sizes and set them aside. Slice the scallions into small rounds and separate the white and green parts.
Start the base: Preheat a medium-sized soup pot over medium heat. Add oil and sauté the white scallion parts with 2 pinches of salt until fragrant, about 8–10 seconds. Don’t let them burn.
Cook the tomatoes: Add the tomatoes with 2 more pinches of salt. Sauté for 2–3 minutes, until very soft and juicy. This will make the soup extra tasty.
Simmer with broth: Pour in the broth, cover, and reduce heat to medium-low. Simmer gently for 8–10 minutes to deepen the flavor.
Prepare eggs and slurry: Whisk the eggs in a measuring cup with spout until small bubbles form. In a separate small bowl, mix the starch with 2 tbsp water to make a slurry.
Check seasoning: Uncover and taste the soup, keeping it on the less salty side since it tastes saltier once cooled.
Thicken the broth: Raise the heat until the soup is at a hot simmer (not a rolling boil). Stir the slurry, then slowly drizzle it in while stirring for about 30 seconds.
Add the eggs: Keep the soup at a gentle simmer. Hold chopsticks (or a fork) against the spout of your measuring cup to guide the flow, then slowly stream the eggs from the center outward in circles from higher up. Let them set for a few seconds before gently stirring in a circular motion to form ribbons.
Finish and serve: Remove from heat. Drizzle with toasted sesame oil and garnish with cilantro and scallion greens. Serve warm or at room temperature.
Notes
Flavor boosters: Add 1 to 1.5 tsp mushroom bouillon, chicken bouillon, or dashi powder for more depth. They can also replace salt.
Starch or no starch: Many Asian soups skip the thickener—leave it out for a lighter, low-carb version.
Egg ribbon sizes: Personally, I like bigger egg flower ribbons (chunkier and fluffier bites). After drizzling the eggs into the hot broth, the more you stir, the finer the ribbons will be. Adjust how much you stir depending on whether you prefer bigger or smaller ribbons.
Add-ins: Try shiitake mushrooms (sauté with the tomato), silken tofu (simmer with the broth), or serve with noodles, wontons, or dumplings.
Vegetarian swap: Use vegetable broth with 1 to 1.5 tsp mushroom seasoning for extra flavor.
Storage: Keeps up to 5 days in the fridge. Reheat gently on the stovetop or microwave.