Preheat oven to 350°F. Grease a 9 x 13-inch baking dish; set aside.
PREPARE THE FILLING:
Melt butter in a large skillet or Dutch oven over medium heat; add mushrooms, onion and celery; sauté 6-8 minutes or until tender. Stir in chicken, rice, soup, sour cream, chives, parsley and thyme. Taste and season with salt and pepper, if desired.
Transfer mixture to the prepared baking dish.
PREPARE THE TOPPING:
In a medium bowl, stir together the crackers and French-fried onions. Add the melted butter and toss to combine. Sprinkle over the top of the casserole.
BAKE THE CASSEROLE:
Cover the casserole and bake for 20 minutes. Remove the cover and bake for 5-7 more minutes, until the filling is hot and bubbly and the topping is lightly toasted. Garnish with fresh parsley, if desired.
Cooking for a smaller family? Cut all of the ingredients in half and bake the casserole in an 8-inch square dish. The rest of the cooking instructions remain the same.
Alternatively, you can divide the casserole ingredients between two 8-inch square baking dishes. Bake one now, and freeze the other for a later meal.
Use a store-bought rotisserie chicken for an easy, quick-prep solution. The rotisserie chicken also adds a lot of flavor to the dish.
Try microwaveable packets of rice for another shortcut, or use leftover rice from a previous meal.
Use full-fat sour cream for the best flavor and texture.
Bake the casserole just until it's heated through. All of the ingredients are already cooked, so you just want to warm it in the oven until bubbly. Don't bake it for too long or it may dry out or get burned on top.