Dice the chicken breast, carrots, celery, and onion into half-inch pieces.
Pour the chicken bone broth into a large pot and bring to a boil over medium-high heat.
Reduce heat to a simmer and add the chicken, carrots, celery, onion, thyme, rosemary, salt, and pepper.
Cover the pot and cook for 10 minutes until the chicken is opaque and the vegetables are slightly softened.
In a small mixing bowl, whisk the egg and then stir in the cassava flour until a thick, sticky dough forms.
Drop the dough by the tablespoonful into the simmering broth, ensuring the dumplings do not touch immediately.
Cover the pot tightly and steam for 8 minutes until the dumplings are set and firm to the touch.
Ladle the soup and dumplings into bowls and top with freshly chopped parsley.