Gather all the ingredients. I recommend making this dish right before you serve.
Beat 1 large egg (50 g each w/o shell) in a bowl or measuring cup.
Cut 1 green onion/scallion into thin, round pieces.
In a small bowl, mix together 2 tsp water and 1 tsp potato starch or cornstarch to make a slurry.
To a saucepan, add 2 cups dashi (Japanese soup stock), 2 tsp sake, and ¼ tsp Diamond Crystal kosher salt.
Add 1 tsp soy sauce. Check the flavor and adjust with more salt, if needed. Then, bring it to a simmer on medium heat.
When simmering, give the slurry mixture another whisk and add it to the dashi.
Stir quickly to distribute the slurry into the dashi. Bring it to a simmer.
Once simmering, slowly pour a thin stream of the beaten egg into the soup in circular pattern, starting from the center and spiraling outward.
Let the egg sit for 20–25 seconds. Then, remove the saucepan from the heat to prevent overcooking.
Serve the soup in individual bowls and garnish with green onion. Enjoy!
