Brown the chicken by heating olive oil in a skillet, adding chicken thighs and cooking until golden brown, about 5 minutes on each side. Set aside.

Sauté the chopped onion and minced garlic in the same skillet until softened, then add diced carrots and celery, cooking for an additional 5 minutes.

Make the gravy by adding butter, followed by flour, stirring for 2 minutes. Gradually add chicken broth and milk, simmering until thickened, about 5-7 minutes.

Return the diced chicken to the gravy and stir in herbs. Simmer gently for another 10 minutes.

Prepare dumplings by mixing flour, baking powder, and salt in one bowl, whisking milk and melted butter in another. Combine gently until just mixed.

Drop spoonfuls of dumpling batter into the simmering gravy. Cover and cook for about 15 minutes without lifting the lid.

Serve hot, ensuring a mix of chicken, gravy, and dumplings in each bowl.