Chicken Spaghetti Casserole

Ingredients (Serves 6 to 8)

For the Base:

• Spaghetti: 12 oz (broken in half for easier serving, or left long if preferred)
• Cooked Chicken: 3 cups, shredded or diced (rotisserie chicken works brilliantly for speed and moisture)
• Butter: 4 tbsp (unsalted)
• Yellow Onion: 1 medium, finely diced
• Bell Pepper: 1 green or red bell pepper, diced (adds subtle sweetness and structure)
• Garlic: 3 cloves, minced
• All-Purpose Flour: ¼ cup (to thicken the sauce)
• Low-Sodium Chicken Broth: 1 ½ cups
• Whole Milk or Half-and-Half: 1 ½ cups (whole milk provides the ideal fat balance for a stable cream sauce)

For the Cheese & Seasonings:

• Cheddar Cheese: 2 cups freshly grated sharp cheddar (gives depth and color)
• Mozzarella Cheese: 1 cup freshly grated mozzarella (adds the classic gooey stretch)
• Seasonings: 1 tsp smoked paprika, ½ tsp garlic powder, ½ tsp onion powder, salt, and freshly cracked black pepper to taste

Step-by-Step Instructions

1. Cook the Pasta (Al Dente)

• Bring a large pot of salted water to a boil. Add the spaghetti and cook 2 minutes shy of the package directions (aiming for firm al dente).
• Why? The pasta will continue cooking and absorbing liquid as it bakes in the oven. If you overcook it initially, it will turn mushy in the casserole. Drain and set aside.

2. Build the Creamy Velouté and Mornay Sauce

• In a large skillet or Dutch oven, melt the butter over medium heat. Add the diced onion and bell pepper, sautéing for 4 to 5 minutes until soft and translucent. Add the minced garlic and cook for 1 minute until fragrant.
• Sprinkle the flour evenly over the vegetables. Stir constantly for 1 to 2 minutes to cook out the raw flour taste (forming a blond roux).
• Slowly whisk in the chicken broth, followed by the milk, whisking vigorously to prevent any lumps from forming. Bring the mixture to a gentle simmer, stirring until it thickens into a smooth, velvety sauce.
• Reduce heat to low. Stir in half of your cheddar and mozzarella cheese until completely melted and smooth. Season with paprika, garlic powder, onion powder, salt, and pepper.

3. Combine Pasta, Chicken, and Sauce

• Add the shredded chicken and the cooked, drained spaghetti directly into the warm cheese sauce.
• Toss gently using tongs until every strand of spaghetti is thoroughly coated in the rich, creamy sauce.

4. Assemble and Bake

• Preheat your oven to 375°F (190°C).
• Grease a 9×13-inch baking dish. Transfer the chicken and spaghetti mixture into the dish, spreading it out into an even layer.
• Top the casserole with the remaining cheddar and mozzarella cheese.

5. Bake to Golden Bubbling Perfection

• Bake uncovered for 20 to 25 minutes, or until the sauce is actively bubbling around the edges and the cheese on top is melted and golden-brown.
• If you want a deeply blistered, crusty top, switch your oven to broil for the final 2 minutes—keeping a close eye so it doesn’t burn.
• Let the casserole rest for 10 minutes before serving. This allows the internal starches and melted cheese to set up, making it much easier to scoop clean portions.

Pro-Tips for Success

• Shred Your Own Cheese: Pre-bagged shredded cheese is coated in cellulose to prevent sticking in the bag, which also prevents it from melting into a smooth, creamy emulsion. Grating a block of sharp cheddar and mozzarella takes 3 minutes and changes the texture entirely.
• Prep Ahead: You can assemble the entire casserole a day in advance, cover it tightly, and store it in the refrigerator. Just add 10 to 15 extra minutes to the baking time if baking straight from cold.