NOTE: This recipe was tested in a 6-quart Instant Pot.
For the stew: Set the Instant Pot to "Saute". Melt the butter in the pot. Add the onion, celery, and carrots and cook, stirring, until they just begin to soften, 4 to 5 minutes, seasoning lightly with salt and pepper and stirring in the poultry seasoning and garlic during the last 30 to 60 seconds of cooking. Press "Cancel". (Freezing instructions begin here.) Lightly season both sides of the chicken with salt and pepper and place in the Instant Pot. Add the broth and bay leaves and stir to combine.
Lock and seal the lid. Cook for 6 minutes at high pressure, then quick release the pressure. (The chicken is done when it registers 165°F internally.) Transfer the chicken to a cutting board and set aside. Remove and discard the bay leaves.
For the dumplings: In a medium bowl, whisk together the flour, baking powder, salt, sugar, and parsley. In a small microwave-safe bowl, microwave the butter and milk together until warm, about 1 minute, then whisk to melt the butter and combine. Stir the wet mixture into the dry mixture until just combined (do not over-mix).
Set the Instant Pot to "Saute" and bring to a boil. Using a soup spoon or tablespoon, scoop out heaping tablespoons of dumpling batter, and drop into the stew. (Wet your hands to prevent sticking and use them to help slide the batter off the spoon.) Try to spread the dumplings out so they cover the whole surface and aren’t on top of one another. Cover the IP loosely with the lid, leaving a crack. Cook for about 11-12 minutes or until the dumplings have doubled in size and a toothpick inserted into the center of a dumpling comes out clean. Press "Cancel".
Meanwhile, shred or chop the chicken into bite-size pieces and set aside.
When the dumplings are done, gently stir the chicken and peas into the stew. Taste and season with salt and pepper as needed.