Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Season the chicken thighs on both sides with salt and pepper.

Add the chicken thighs to the pot in a single layer and sear for 3-4 minutes per side until golden brown. They do not need to be cooked through at this stage. Remove and set aside on a plate.

Reduce heat to medium. Add the diced onion, carrots, and celery to the pot. Sauté for 5-6 minutes, stirring occasionally, until the vegetables begin to soften and the onion is translucent.

Add the minced garlic, dried thyme, dried parsley, and onion powder. Stir and cook for 1 minute until fragrant.

Sprinkle the 3 tablespoons of flour over the vegetables and stir well to coat. Cook for 1-2 minutes, stirring constantly, to eliminate the raw flour taste.

Gradually pour in the chicken broth while stirring continuously to prevent lumps. Add the milk or half-and-half and stir to combine. Return the seared chicken thighs to the pot, nestling them into the broth.

Bring the soup to a gentle boil, then reduce heat to low-medium. Simmer uncovered for 20 minutes, or until the chicken is fully cooked through and tender.

Remove the chicken thighs and transfer to a cutting board. Using two forks, shred the chicken into bite-sized pieces. Return the shredded chicken to the pot and stir to combine. Taste and adjust seasoning with additional salt and pepper as needed.

In a large mixing bowl, whisk together the flour, baking powder, salt, and garlic powder until combined.

Add the melted butter and milk to the dry ingredients. Stir with a fork or spatula just until a soft, shaggy dough forms. Do not overmix — some lumps are perfectly fine. Fold in the chopped fresh parsley if using.

Bring the soup back up to a gentle simmer over medium heat. If adding frozen peas, stir them in now.

Using a large spoon or cookie scoop, drop rounded tablespoon-sized portions of dumpling dough directly onto the surface of the simmering soup. Work quickly, spacing them slightly apart — the dumplings will puff and expand as they cook.

Once all the dumplings are in the pot, immediately place the lid on and reduce the heat to low. Do not lift the lid. Cook for 15 minutes, allowing the steam to cook the tops of the dumplings through.

After 15 minutes, lift the lid and check that the dumplings are cooked through — they should look set on top, not wet or glossy. Insert a toothpick into the center of one dumpling; it should come out clean.

Serve immediately, ladling the soup and dumplings into wide bowls. Garnish with fresh parsley and a crack of black pepper.