Melt 4 tablespoons of butter in a large pot over medium heat. Add 1 chopped onion and sauté for 3-4 minutes until translucent. Stir in 2 cups of chopped celery and 2 cups of chopped carrots, sautéing for another 2-3 minutes until they start to soften.

Add 1.5 pounds of boneless chicken thighs and breasts, 1 tablespoon of fresh thyme leaves, and 1 whole bay leaf to the pot. Pour in 6 cups of chicken stock and season with salt and pepper. Bring to a boil, reduce heat to low, cover, and simmer for 20-25 minutes until chicken is fully cooked.

In a mixing bowl, combine 2 cups of flour, 1 tablespoon of baking powder, and 1 teaspoon of salt. Cut in 1/2 cup of vegetable shortening until the mixture resembles coarse crumbs. Gradually stir in 1 cup of buttermilk until a soft, slightly sticky dough forms.

Turn the dough out onto a floured surface and roll to about 1/2 inch thick. Cut into 1x1.5-inch pieces resembling thick noodles. Set aside.

Carefully remove cooked chicken from the pot and place on a plate to cool slightly. Drop dumpling pieces into the simmering broth, one handful at a time. Cover and simmer for 8-10 minutes until dumplings are fluffy.

Shred the chicken into bite-sized pieces and return to the pot. Stir in 1/4 cup of chopped parsley. Adjust seasoning with salt and pepper as needed. Serve warm.