Heat up the chicken stock with salt, pepper, sugar added to taste, and the sesame oil.
Make a slurry out the cornflour, by either mixing it with a little bit of chicken stock or water. Keep the egg ready by beating it and adding a tsp of the cornflour slurry to it.
Once the stock starts boiling, add the cornflour slurry. Constantly stir the soup till it thickens.
Now using a fork pour the egg into the boiling soup, in a circular fashion, stirring constantly so that the egg forms thin strands.
Simmer for a minute or two till the egg gets cooked. Garnish with finely chopped scallions and/or coriander leaves.