Old Fashioned Chicken and Rice

Name: Old Fashioned Chicken and Rice
Prep time: 5 min
Cook time: 35 min
Total time: 40 min
Cuisine: American
Ingredients: 6 tablespoons butter divided; 1 large onion diced; 3 ribs celery diced; 3 boneless skinless chicken thighs (or 2 breasts) (cut into 1” pieces); 3 cups chicken stock; 1 ½ cups rice (long grain white, basmati, or brown); 2 teaspoons salt; 1 teaspoon ground black pepper; 2 tablespoons chopped fresh parsley (optional)