Ingredients
Equipment
Method
Prep & cook the pasta
- Preheat the oven to 375°F (190°C). Set out a greased 9x13-inch baking dish for later.
- Cook the spaghetti according to package directions and drain. Leave it in the colander so excess water doesn’t thin the sauce.
Make the Parmesan sauce
- Melt the butter in a large skillet over medium heat. Swirl until the butter is fully melted and lightly foamy.
- Add the mushrooms and cook until softened. Cook for several minutes, stirring, until they give off moisture and look tender.
- Stir in the minced garlic and cook for 30 seconds. Keep stirring so it becomes fragrant without browning.
- Sprinkle the flour over the mushrooms and stir for 1 minute. The mixture should look slightly thickened and paste-like.
- Gradually whisk in the chicken broth, milk, and cream. Whisk until smooth and no floury lumps remain.
- Simmer until the sauce thickens. Look for a silky consistency that coats the back of a spoon.
- Stir in the Parmesan cheese, Italian seasoning, salt, and black pepper. Continue stirring until the cheese melts and the sauce turns glossy.
Assemble & bake
- Stir in the chicken and cooked spaghetti. Mix until everything is evenly coated.
- Transfer the mixture to the greased 9x13-inch baking dish. Spread into an even layer.
- Top with the shredded mozzarella cheese. Cover the surface in a uniform layer.
- Bake for 25–30 minutes until bubbly and golden. The edges should bubble and the top should look lightly browned.
- Garnish with the chopped parsley before serving. Sprinkle on top right after baking for a fresh green finish.
Notes
For the thickest, most sliceable casserole, simmer the sauce until it clearly coats a spoon before adding chicken and spaghetti. Store leftovers covered in the refrigerator for up to 3–4 days; freeze baked portions for up to 2 months and thaw overnight in the fridge, then reheat until steaming. For a lighter option, use reduced-fat mozzarella and swap whole milk for 2% milk.