Put the chicken strips, chicken stock, and heavy cream into a large saucepan and bring to a boil over a low heat. Reduce the heat slightly and simmer for about 20 minutes. Season the soup with salt and pepper to taste.
Meanwhile, cook the vermicelli in lightly salted boiling water for 10-12 minutes, until just tender. Drain the pasta and keep warm.
In a small bowl, mix together the cornstarch and milk to make a smooth paste. Stir the cornstarch paste into the soup until thickened. Add the corn and vermicelli to the pan and heat through.
Transfer the soup to a warm tureen or individual soup bowls, garnish with scallions, if desired, and serve immediately.