Season chicken pieces with Morton’s seasoning blend.

Melt 3 tablespoons butter in a large Dutch oven over medium-high heat. Add chicken, skin sides down, and cook until golden brown, about 6–8 minutes per side.

Add broth and water to the pot, bring to a boil. Add onion, poultry seasoning, garlic, salt, and pepper. Simmer covered for 20 minutes. Then add carrots and celery, and simmer partially covered until vegetables are tender, about 20 more minutes.

In a large bowl, mix together flour, baking powder, and salt. In a medium bowl, whisk egg and buttermilk together. Cut chilled butter into the flour mixture until crumbly. Add the buttermilk mixture and stir until combined. Wrap dough with plastic wrap and refrigerate for 30 minutes.

Pat dough to approximately 1-inch thickness on a floured surface and fold edges inward. Repeat until dough comes together. Cut dough into 2x2-inch squares.

Remove cooked chicken from the broth and let rest under foil. Skim fat from broth. Bring broth to a gentle boil and drop dumpling squares in. Simmer, uncovered, until dumplings rise to the surface, about 10 minutes. Return chicken to the pot and cook for another 5 minutes.