Prepare the Oven and Squash

• Preheat the oven to400°F (200°C).
• Lightly grease a 9 × 13-inch baking dish.
• Place the cubed butternut squash in a large bowl.
• Toss with olive oil, smoked paprika, thyme, rosemary, salt, and black pepper.
• Spread the squash on a baking sheet and roast for 20–25 minutes, until slightly tender but not completely soft.

Prepare the Creamy Sauce

• In a large skillet, cook the diced onion over medium heat for 4–5 minutes until softened.
• Add the minced garlic and cook for another 30 seconds.
• Stir in the chicken broth, heavy cream, and sour cream.
• Simmer gently for 2–3 minutes until slightly thickened.
• Remove from the heat and stir in the Parmesan and mozzarella cheese until creamy.

Assemble the Casserole

• Reduce the oven temperature to375°F (190°C).
• Spread the roasted butternut squash evenly in the prepared baking dish.
• Add the cooked shredded chicken and gently mix with the squash.
• Pour the creamy sauce over the mixture, making sure everything is coated.
• Sprinkle the cheddar cheese evenly over the top.

Add the Crispy Topping

• In a small bowl, combine the breadcrumbs with melted butter.
• Sprinkle the mixture evenly over the casserole.
• Add a little extra Parmesan if desired.

Bake Until Golden

• Bake uncovered for 20–25 minutes, until the casserole is bubbling around the edges and the topping is golden brown.
• If the topping needs more color, broil for 1–2 minutes, watching carefully.
• If using freshly cooked chicken, ensure it has reached an internal temperature of165°F (74°C)before adding it to the casserole.