Bring the broth, chicken, carrot, celery, and onion to a boil in a pot over medium-high heat. Turn down to a simmer, and cook until the chicken reaches an internal temperature of 160°F. Remove the chicken from the heat and set aside.
Using 2 forks pull the chicken apart in opposite directions to shred. Return the shredded chicken to the pot.
Add the peas and tortellini to the pot and return to a simmer for about 5 minutes or until the tortellini is tender. (The tortellini will start to float when they are cooked.)
In a bowl mix together the flour with an equal amount of water (or a little more if needed) to form a smooth paste.
Add the heavy cream and bring to a simmer. Slowly stir in the flour/water mixture until the soup becomes thickened and creamy.
Taste and adjust the seasoning with salt and pepper. Ladle into bowls and sprinkle with parmesan to serve.