Melt the butter in a large and deep oven safe pan or dutch oven over medium-low heat.
Add in the diced carrots, celery, and onion and stir to coat with butter. Cover the pot with a lid and allow the vegetables to cook, stirring occasionally for 6 minutes.
Remove the lid and add the garlic to the pot, stir constantly for about 30 seconds.
Add the thyme, ground mustard, cumin, cayenne, flour, and salt and pepper to taste to the pot.
Cook stirring constantly for 2 minutes to cook the flour.
Slowly pour in the chicken broth while stirring constantly until smooth.
Add the noodles and shredded chicken to the pan. Simmer, stirring occasionally to submerge the noodles under the broth until cooked through, about 8-10 minutes.
Serve immediately as is, or follow directions to make the topping.
FOR THE TOPPING:
Preheat the oven to broil/high.
Combine the melted butter in a medium bowl with the panko, parsley, and salt.
Top the casserole evenly with the breadcrumb mixture and broil for 2-3 minutes just until golden brown.
NOTE ON EQUIPMENT:
This recipe was made using a 12 inch, deep, oven safe skillet. You can also use a dutch oven. If you don't have either, you can pour into a 9x13 inch baking dish before adding the topping, then bake.NOTE ON SUBSTITUTIONS/ADDITIONS:
Vegetable broth will work in place of chicken broth.
You can add 1 cup of your favorite shredded cheese to this casserole if desired. Stir in after the noodles are cooked, before adding the topping.
If you don't have Panko, you can use regular plain or Italian breadcrumbs for the topping.