Add 1½ cups of chicken broth to a 3 cup earthenware bowl. Boil over medium high heat.
Add 3 cracked eggs and 1 egg yolk to a bowl.
Add 1 ts fish sauce and 2 tbs chopped green onion to the eggs. Beat well.
When the chicken broth starts boiling, lower the heat to a simmer.
Add the egg mixture to the simmering broth and stir it well with a fork well for 10 seconds.
Close the lid and simmer another 4-5 minutes until the egg mixture sizzles and has a texture like soft tofu.
Open the lid and turn off the heat. Drizzle 2 ts sesame oil and sprinkle 1 tbs chopped green onion over top.