1. Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish with butter or non-stick spray.
2. In a large skillet, melt the butter over medium heat. Add the chopped onion and cook until translucent and fragrant, about 5 minutes. Stir in the minced garlic and cook for another minute, being careful not to burn it.
3. In a large bowl, combine the cooked chicken, prepared stuffing, and sautéed onions and garlic. Toss gently to mix everything evenly.
4. In a separate bowl, whisk together the chicken broth, sour cream (or Greek yogurt), and cream of mushroom soup until smooth. Stir in the dried thyme, sage, salt, and pepper.
5. Pour the creamy sauce over the chicken and stuffing mixture. Using a spoon or spatula, gently fold everything together until well coated.
6. Transfer the mixture to your prepared baking dish, spreading it out evenly. Sprinkle the shredded cheddar cheese evenly on top, if using.
7. Bake uncovered for 30-35 minutes, or until the casserole is bubbly around the edges and the cheese is melted and golden.
8. Remove from the oven and let it rest for about 5-10 minutes before serving. This helps the casserole settle and makes it easier to serve.
9. Garnish with freshly chopped parsley for a pop of color and freshness.

A little tip from my kitchen: If you want a crispier top, you can broil the casserole for the last 2-3 minutes. Just keep a close eye on it so it doesn’t burn. I’ve found that this step adds a lovely texture contrast that my girls absolutely love.