In a mixing bowl, whisk together the flour, baking powder, and salt for the dumplings.
Cut in the cold butter until the mixture resembles coarse crumbs.
Stir in the milk just until combined and set aside.
In a large pot, sauté the chopped carrot, celery, and onion until softened, about 5 minutes.
Add the minced garlic and cook for an additional 1 minute.
Pour in the chicken broth and bring to a boil.
Lower the heat and add the shredded cooked chicken and dried thyme.
Drop spoonfuls of the dumpling dough into the simmering broth.
Cover the pot and cook for 15 minutes, or until the dumplings are cooked through.
Season the soup with salt and pepper to taste.
Serve hot, garnished with fresh parsley.