In a large stock pot or dutch oven, melt 2 tablespoons of the butter. Use this to sauté the celery and onion until soft and onions are translucent.
Add the frozen veggies, stirring until they are thawed.
Add the remaining 2 tablespoons of butter, and the flour, stirring until flour is incorporated.
Slowly add the broth, stirring continuously to avoid lumps.
Allow to simmer 3-4 minutes until mixture begins to thicken. Then add the half & half or milk, stirring until a creamy sauce is formed.
Add the salt & pepper, thyme and sage.
Add the cooked turkey or chicken and allow to simmer until warmed through.
Turn off the heat, and add the shredded cheese. Stir until cheese is melted and smooth.
Serve immediately, with more cheese sprinkled on top for garnish, and crusty bread for dipping.