Finely chop the onion, celery, and carrots, and mince the garlic.
Heat the butter in a large stockpot over medium-high heat. Add the chopped veggies and sauté for about 5-7 minutes, or until tender and fragrant.
Stir in the thyme, sage, salt, pepper, and cayenne (if using), and cook for another minute.
Add the vegetable stock, bay leaves, and parmesan rind (if using), and bring the mixture to a boil. Stir frequently to prevent the parmesan rind from sticking to the pot.
Add the shredded chicken and stelline pasta, then reduce the heat and let it simmer for 8-12 minutes, or until the pasta is cooked through.
Stir in the lemon juice, taste, and adjust the seasoning if needed.
Garnish with fresh parsley and serve immediately!