Preheat Oven & Prep Dish: Preheat your oven to 375°F (190°C). Lightly grease a standard 9x13-inch ceramic baking dish with cooking spray or butter.

Sauté Aromatics & Mushrooms: In a large deep skillet or Dutch oven, melt 2 tablespoons butter over medium heat. Add diced onion, chopped celery, and sliced cremini mushrooms. Sauté for 6-8 minutes until the mushrooms are golden browned and vegetables are tender. Stir in minced garlic and cook for 1 minute until fragrant. Transfer veggies to a bowl and set aside.

Make Velvety Cream Sauce: In the same skillet over medium heat, melt 3 tablespoons butter. Whisk in all-purpose flour and cook for 1-2 minutes until lightly golden and nutty. Gradually pour in chicken broth and heavy cream while whisking constantly to prevent lumps. Stir in chopped thyme, garlic powder, onion powder, salt, and black pepper. Simmer for 3-4 minutes until thick and velvety.

Melt Cheese & Combine: Remove skillet from heat. Stir in 1 cup of shredded sharp cheddar cheese until fully melted and smooth. Fold in cooked wild rice blend, shredded chicken, and sautéed mushroom-onion mixture until evenly coated in luxurious cream sauce.

Assemble Casserole: Transfer chicken and rice mixture into the prepared 9x13-inch baking dish, spreading it into an even layer. Sprinkle the remaining 1/2 cup shredded cheddar cheese evenly over top.

Add Crunchy Panko Topping: In a small bowl, toss panko breadcrumbs, melted butter, and sliced almonds together. Scatter evenly over the cheese layer.

Bake to Golden Perfection: Bake uncovered at 375°F (190°C) for 22-25 minutes until the casserole is bubbling vigorously around the edges and the panko topping is deeply golden and crisp. (Broil on HIGH for 1-2 minutes if extra browning is desired).

Rest, Garnish & Serve: Let the casserole rest for 5-10 minutes to allow the sauce to settle. Garnish with fresh chopped thyme and parsley, then scoop generous squares and serve piping hot!