Heat the olive oil in a deep skillet or Dutch oven over medium heat. Once hot, add the boneless, skinless chicken thighs and brown them on each side. The chicken does not need to be cooked through at this point; just focus on getting a nice golden color on the outside. Once browned, transfer the partially cooked chicken to a clean bowl to rest.

In the same skillet (without cleaning it), add the diced onion and minced garlic. Sauté over medium heat, stirring to dissolve the browned bits on the bottom of the pan as the onions cook. When the onions start to soften, add the diced carrots and diced celery, continuing to sauté everything together for about five more minutes or until the vegetables have softened.

Add the butter to the skillet and let it melt. Sprinkle the flour over the vegetables and stir until the butter has melted and created a thick paste (roux) that coats the vegetables. Cook and stir this mixture for about two minutes to get rid of the raw flour taste. Next, add the dried parsley, dried thyme, dried rosemary, dried sage, salt, black pepper, chicken broth, and whole milk. Turn the heat up to medium-high and stir continuously until the mixture comes up to a gentle simmer and thickens into a flavorful gravy.

Dice the browned chicken thighs from Step 1 into bite-sized pieces. Return the diced chicken to the skillet with the thickened gravy and vegetables. Cover with a lid and let it simmer gently over medium heat while you prepare the dumplings. I like to let the chicken absorb the flavors of the gravy during this stage.

In a mixing bowl, combine the flour, dried parsley, granulated sugar, salt, baking powder, garlic powder, and black pepper. Pour in the milk and melted butter, and gently stir the ingredients just until a soft, scoopable batter forms. Be careful not to overmix; a light touch helps keep the dumplings fluffy. Personally, I find that letting the batter rest for a minute helps hydrate the flour and leads to better dumplings.

Remove the lid from the chicken and gravy mixture, which should be gently simmering. Using two spoons, drop 2-tablespoon dollops of dumpling batter onto the surface of the simmering gravy, creating about 12 dumplings. Make sure the gravy continues to simmer, then place the lid back on the skillet and allow the dumplings to steam-cook for 15 minutes. Avoid lifting the lid during this time to ensure the dumplings stay light and fluffy. Once cooked, the dumplings will have doubled in size and should be cooked through. Serve hot and enjoy!