Preheat over to 450 degrees
Melt the butter in a large heavy pot over medium high heat until hot.
add the carrots, celery, and onions and Seaton with 1 tsp salt and 3/4 tsp pepper.
Cook, stirring occasionally, until the vegetables are golden, about 12 minutes.
Stir in the flour, and then whisk in the broth and mix and bring to a boil, whisking
Boil until slightly thickened , about 3 minutes.
Stir in the chicken
Transfer to a 2 quart baking dish.
Pulse the tots in a food processor with the thyme until medium ground
Scatter over the top of the casserole and bake until the filling is bubbling and the topping is golden and crisp, 20-25 minutes.
Let stand 10 minutes before serving.