Preheat oven to 350-degree F.

Spray a 9X13 pan with kitchen pan spray.

Heat chicken stock to hot then hold.

In a medium non-stick pot or large sauce pan, melt butter over medium heat and add onion, celery, carrot, garlic, thyme, salt and pepper and cook three minutes.

Add the flour and cook two minutes, then add all of the hot stock, mixing to combine with a wooden spoon or sturdy rubber spatula.

Turn the heat down to medium low and simmer until vegetables are soft, about 5-10 minutes.

Remove half of this mixture and puree with a blender or an immersion blender then pour back into the pan with the half that is not pureed. Add the tub of sour cream and mix to combine.

Set 1 ½ cups of the shredded cheese aside to top the casserole.

In a large bowl, mix the frozen potatoes, the sauce and what’s left of the Colby Jack cheese. Scrape into the prepared casserole dish and top with the remaining cheese.

Bake uncovered for 45 minutes then broil the top to brown.

Serve immediately.