Step 1: Prepare the Ingredients

1. Shred or dice the leftover turkey into bite-sized pieces and set aside.
2. Gather and chop your leftover vegetables or cook fresh ones if needed. If using rice, pasta, or stuffing, ensure it’s cooked and ready to add to the casserole.

Step 2: Make the Sauce

1. In a medium saucepan, melt the butter over medium heat. Once melted, whisk in the flour to form a roux. Cook for 1-2 minutes until lightly golden.
2. Gradually add the turkey or chicken broth, whisking constantly to prevent lumps. Then stir in the milk or cream.
3. Add the garlic powder, onion powder, thyme, salt, and pepper. Simmer the sauce for 3-4 minutes, stirring occasionally, until thickened. Taste and adjust seasoning as needed.

Step 3: Assemble the Casserole

1. Preheat your oven to 375°F (190°C).
2. In a greased 9×13-inch baking dish, layer the turkey, vegetables, and optional rice or stuffing. Pour the prepared sauce evenly over the top, ensuring everything is well-coated.
3. Sprinkle the shredded cheese over the casserole.

Step 4: Prepare the Topping

1. In a small bowl, mix the breadcrumbs (or crushed crackers) with the melted butter. Spread the mixture evenly over the cheese layer.

Step 5: Bake the Casserole

1. Place the casserole in the preheated oven and bake for 30-35 minutes, or until the topping is golden brown and the casserole is bubbling around the edges.
2. Remove from the oven and let it rest for 5 minutes before serving.

Step 6: Garnish and Serve

1. Garnish the casserole with fresh parsley or a sprinkle of paprika for color. Serve warm with a side salad or bread rolls.