Place chicken in a large pot and cover with 12 cups water. Add onion, carrots, garlic, celery, bay leaves, and thyme. Add 1 teaspoon salt (you'll add more later). Ensure the chicken is covered with water. Bring to a boil and then reduce heat to low. Cover and simmer for 1 hour and 30 minutes.

Carefully remove the chicken from the pot and transfer it to a large bowl.

Turn the heat on the broth to medium. Allow it to rapid-simmer for 30 minutes so that it reduces further. The broth will be a very deep golden brown. You should be left with between 8–10 cups of broth.

Strain the broth through a fine-mesh sieve into a very large bowl. Discard solids.

Carefully wash out the pot and return it to the stovetop.

Turn the heat on the pot to medium. Add the mushrooms and let them cook in the dry pot until they release their liquid, about 6–7 minutes. No need to fuss over them or stir them too frequently. Allow them to release their liquid and for that liquid to evaporate.

Continue cooking until they begin to brown, an additional 3–4 minutes.

Melt the butter into the mushrooms and cook for 2–3 minutes, occasionally stirring. They will begin turning golden brown.

Add the diced onion, carrots, parsnip, and celery and toss to combine. Cook for 6–7 minutes, often stirring until they soften. Season all over with salt and pepper.

Sprinkle the flour over the vegetables and toss to coat. Toast the flour for 1–2 minutes.

Ladle 1 cup of the reserved broth from the bowl and whisk to incorporate. Continue adding 1–2 ladlefuls until most of the broth has been added. Pour in the remaining broth and the chicken.

Bring to a boil and then reduce heat to low and simmer for 20 minutes or until the soup is thickened. Taste and season to your preferences.

Combine flour, baking powder, and baking soda in a bowl. Add the cold butter and work it into the flour until it's crumbly. Season with a pinch of salt and a few cracks of pepper.

Pour in the ½ cup buttermilk and stir to combine. It's okay if it becomes a little doughy or seems slightly dry.

Pour the heavy cream into the soup and add the frozen peas. Turn the heat to medium-low.

Before cooking the dumplings, stir 2 tablespoons more buttermilk into the dumpling mixture. It should feel relatively loose and still wet.

Using a tablespoon, drop spoonfuls of the dumplings into the pot.

Cover and simmer for 10 minutes. Test dumplings with a toothpick to make sure it comes out clean. Turn off the heat.

Ladle the soup and dumplings into bowls. Garnish with freshly minced chives. Enjoy!