Ingredients
Equipment
Method
Preheat and cook pasta
- Preheat oven to 375°F (190°C). This sets the temperature so the casserole bakes evenly right after assembly.
- Cook spaghetti according to package directions and drain. Keep it hot so it folds into the sauce smoothly.
Make the creamy sauce
- Melt butter in a large skillet over medium heat. The butter should look glossy before you add the mushrooms.
- Add mushrooms and cook for 5 minutes. Stir occasionally until the mushrooms release moisture and soften.
- Stir in garlic and cook for 30 seconds. Cook just until fragrant, not browned.
- Whisk in flour and cook for 1 minute. The mixture should look slightly thickened and smooth.
- Gradually add chicken broth and milk while whisking. Keep whisking to prevent lumps.
- Simmer until the sauce thickens. You want a pourable, creamy consistency that coats the back of a spoon.
- Stir in sour cream, mozzarella, Parmesan, Italian seasoning, salt, and pepper. Mix until the cheeses melt and the sauce turns smooth and glossy.
Assemble and bake
- Fold in cooked chicken and spaghetti. Mix until everything is coated in the creamy sauce.
- Transfer mixture to a greased 9×13-inch baking dish. Spread into an even layer so it bakes consistently.
- Sprinkle breadcrumbs evenly over the top. Covering the surface helps create a golden, crisp finish.
- Bake for 25–30 minutes until bubbly and golden. Look for active bubbling around the edges and browned breadcrumb peaks.
- Garnish with parsley and serve warm. Let it rest briefly so slices hold together.
Notes
For best texture, bake on the center rack and wait until the casserole is fully bubbly before removing. Refrigerate leftovers in an airtight container up to 3 days; reheat at 350°F (175°C) until hot and creamy throughout. Freezing: yes—freeze baked and cooled portions up to 2 months, thaw in the fridge and reheat until warmed. For a lighter option, use low-fat milk and a light sour cream while keeping the baking time the same.