Pat the chicken thighs dry with paper towels. Season them with salt and pepper. This step helps build flavor. Keep them ready while you prepare the vegetables.

Place a large casserole pot on medium heat. Add olive oil and let it warm up. Do not rush this step. Warm oil helps cook the chicken evenly.

Add chicken thighs to the pot. Cook for about 5 minutes on each side. They should turn golden brown. Remove them and set aside for later use.

In the same pot, add onion, carrots and celery. Stir gently for about 5 minutes. The vegetables should soften and release a sweet smell.

Add minced garlic to the vegetables. Cook for one minute only. Garlic cooks fast, so do not burn it. Stir gently to mix the flavors.

Sprinkle flour over the vegetables. Stir well until everything is coated. Cook for two minutes. This helps thicken the sauce later.

Slowly pour in chicken stock while stirring. This avoids lumps. Keep stirring until the mixture becomes smooth and slightly thick.

Pour in milk or cream for richness. Stir well to combine. The sauce will become creamy and smooth. This is the base of your casserole.

Add thyme, parsley, salt and pepper. Stir everything together. Taste the sauce and adjust seasoning if needed.

Place the browned chicken back into the pot. Make sure it is covered with sauce. This helps the chicken stay juicy and tender.

Add sliced mushrooms and halved potatoes. Stir gently to mix. These ingredients make the dish more filling and hearty.

Cover the pot and place it in a preheated oven at 180°C. Bake for about 60 minutes. The chicken will become soft and flavorful.

Remove from the oven carefully. Check if the chicken is fully cooked. Sprinkle fresh parsley on top. Serve hot and enjoy your meal.