To prepare soup: To a medium Dutch oven set over medium heat, add 2 tablespoons of butter. When butter melts and foam subsides, add the diced chicken; cook, stirring occasionally until chicken is browned, about 5 minutes. Using a slotted spoon, remove chicken and add onion, celery and carrot; cook, stirring occasionally until softened, about 5 to 7 minutes. Add the remaining 2 tablespoons of butter and stir. When the butter has melted, add flour, stir vigorously to blend with vegetables and butter. Cook for 2 to 3 minutes without letting flour brown. Add 1 cup of chicken broth and whisk until mixture is smooth, then whisk in the remaining broth. Bring soup to a simmer.

To a medium skillet set over high heat, add oil. When the oil is shimmering, add mushrooms and cook, stirring occasionally until they are a deep golden brown color, about 8 minutes; taste and adjust seasoning with salt and pepper. Add mushrooms and thyme to the simmering soup. Taste and adjust seasoning with salt and pepper. Continue to simmer soup while preparing dumplings.

To prepare dumpling dough: To a large mixing bowl, whisk flour, baking powder, chives, parsley and salt. In a separate bowl, whisk melted butter, egg and buttermilk until smooth. Slowly pour wet ingredients into dry ingredients and with a wooden spoon, stir until just combined. Cover with plastic wrap and set aside.

To finish soup: Add peas, chives and parsley to soup; stir to combine. Taste the soup and adjust seasoning with salt and pepper. Drop heaping tablespoons of dumpling dough onto the surface of the soup. Cover Dutch oven and simmer until dumplings are firm, about 20 to 25 minutes.

To serve: Divide soup and dumplings between 8 shallow serving bowls. Garnish with chopped herbs.