Preheat oven to 350 degrees F
In a saucepan, saute onions and celery in butter until soft, about 3-4 minutes
Add chicken to the saucepan, season with salt and pepper
Cook until chicken is slightly brown and cooked through, about 5 minutes
In a large bowl, combine the rice and seasoning packet
Pour in chicken broth and stir
Add soup and sour cream, whisk together until well combined
Pour into a 13×9 baking dish
Add chicken mixture, and press down to cover with soup mixture
Crush crackers and add to a small bowl
Melt butter and add to the crackers
Mix well and sprinkle on top of the casserole
Bake at 350 degrees F for 30-40 minutes or until hot and bubbling