In a large pot, combine the chicken broth, cooked chicken, diced onion, sliced carrots, sliced celery, garlic powder, onion powder, thyme, salt, and pepper.
Bring to a simmer over medium heat and cook for about 15 minutes until the vegetables are tender.
In a mixing bowl, whisk together the flour, baking powder, and salt.
Add the melted butter and ¾ cup milk, stirring until just combined. The dough will be thick.
Drop spoonfuls of the dumpling batter into the simmering chicken mixture.
Cover the pot and let the dumplings cook for 15-20 minutes without lifting the lid.
Once the dumplings are done, stir in 1 cup of milk to create a creamy consistency.
Adjust seasoning if needed and serve hot.