1. In a heavy skillet or Dutch oven, heat the oil or butter over medium heat. Gradually whisk in the flour and cook, stirring constantly, until the roux turns deep golden brown, about 8–10 minutes. 2. Add the onion, bell pepper, and celery to the roux. Cook about 5 minutes until softened. Add garlic and cook another minute. 3. Stir in tomato paste and Cajun seasoning. Slowly whisk in chicken stock until smooth. Bring to a simmer. 4. Season chicken pieces with salt and pepper, then add them to the sauce. Cover and simmer over low heat for 25–30 minutes, stirring occasionally, until chicken is tender and sauce has thickened. 5. Serve over cooked white rice, garnished with fresh parsley and hot sauce if desired.