Combine the flour, baking powder, baking soda, salt, garlic powder, and sugar in a medium bowl.
Add the milk, sour cream, and melted butter. Use a folding motion to combine and form a dough, but don’t overmix or they will be dense.
Add the chicken back to the soup along with any juices from the plate. Stir to combine and reduce heat to low. (If using leftover chicken, add it now.)
Use a small cookie scoop and carefully place the dumplings over the soup in an even layer. Spoon a little liquid over each one.
Cover tightly and increase heat slightly to bring it to a gentle simmer. Set a timer for 15 minutes, don’t lift the lid during this time, the dumplings need to steam.
Open the lid and insert a toothpick into the middle of a dumpling to check for doneness. If it comes out clean, it’s ready. If not, cover and simmer for a few more minutes.
Once the middle is set, garnish with parsley and serve!