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Creamy Garlic Parmesan Baked Spaghetti Alfredo Casserole

There is something wonderfully comforting about a bubbling pasta casserole coming out of the oven, especially when it is coated in a rich garlic Parmesan Alfredo sauce. This Creamy Garlic Parmesan Baked Spaghetti Alfredo Casserole takes familiar spaghetti and transforms it into a creamy, cheesy dish with golden edges and plenty of flavor in every bite.

Instead of serving spaghetti with a sauce on top, this recipe combines everything before baking. The pasta absorbs some of the creamy Alfredo sauce while it cooks in the oven, creating a casserole that is rich without being overly complicated. Garlic adds warmth, Parmesan brings a savory depth, and mozzarella creates that irresistible melted-cheese topping.

It is a practical recipe for a family dinner, weekend meal, or potluck because most of the preparation can be done before the casserole goes into the oven.

Why You’ll Love This Recipe

This baked spaghetti has several things going for it:

Creamy and comforting: Alfredo sauce gives the spaghetti a silky texture.
Garlic-forward flavor: Fresh garlic adds much more character than a heavily seasoned sauce.
Plenty of cheese: Parmesan goes into the sauce while mozzarella creates a bubbly topping.
Easy preparation: The pasta and sauce come together in one baking dish.
Make-ahead friendly: You can assemble the casserole ahead of time and bake it when needed.
Family-style serving: It slices and scoops easily, making it ideal for sharing.

Ingredients

For the Spaghetti

12 ounces spaghetti
1 tablespoon salt, for the pasta water
1 tablespoon olive oil or butter

For the Garlic Parmesan Alfredo Sauce

4 tablespoons unsalted butter
4 cloves fresh garlic, finely minced
2 tablespoons all-purpose flour
2 cups whole milk
1 cup heavy cream
1 cup freshly grated Parmesan cheese
½ teaspoon Italian seasoning
½ teaspoon salt, or to taste
¼ teaspoon black pepper
¼ teaspoon onion powder
A small pinch of red pepper flakes, optional

For Assembly

1 cup shredded mozzarella cheese
½ cup additional Parmesan cheese
2 tablespoons chopped fresh parsley
A little extra black pepper, optional

Step 1: Prepare the Oven and Baking Dish

Start by preheating your oven to 375°F (190°C).

Lightly grease a 9×13-inch baking dish with butter or cooking spray. Greasing the dish helps prevent the creamy pasta from sticking and makes serving much easier later.

Set the prepared dish aside while you make the pasta and sauce.

Step 2: Cook the Spaghetti

Bring a large pot of water to a rolling boil. Add the salt, then place the spaghetti into the water.

Cook the pasta according to the package directions, but stop cooking it about 1–2 minutes before it reaches full doneness.

The spaghetti should still have a slight firmness to it. It will continue cooking in the oven, and slightly undercooking it at this stage helps prevent the finished casserole from becoming mushy.

Before draining, reserve about ½ cup of the pasta water.

Drain the spaghetti well and toss it with the olive oil or butter to keep the strands from sticking together.

Step 3: Build the Garlic Parmesan Sauce

While the pasta is cooking, prepare the Alfredo sauce.

Place a large saucepan over medium heat and add the butter. Once melted, add the minced garlic.

Cook the garlic for about 30–60 seconds, stirring frequently. You want it fragrant and lightly softened rather than deeply browned. Burned garlic can make the sauce taste bitter.

Sprinkle the flour over the butter and garlic. Whisk continuously for about 1 minute. This creates a simple roux that will help thicken the sauce.

Slowly pour in the milk while whisking. Follow with the heavy cream.

Continue whisking until the mixture becomes smooth.

Step 4: Season the Sauce

Add the Italian seasoning, onion powder, salt, black pepper, and optional red pepper flakes.

Allow the sauce to gently simmer for several minutes, stirring frequently.

You are looking for a sauce that is creamy enough to coat the back of a spoon but still loose enough to mix easily with the spaghetti.

Avoid boiling the sauce aggressively. A gentle simmer helps maintain a smooth texture.

Step 5: Add the Parmesan

Lower the heat before adding the Parmesan cheese.

Gradually stir in the freshly grated Parmesan, allowing each addition to melt before adding more.

The cheese will thicken the sauce and give it the distinctive savory flavor associated with Alfredo.

If the sauce becomes thicker than expected, add a splash of the reserved pasta water. The starchy water can loosen the sauce while helping it cling to the spaghetti.

Taste the sauce and adjust the seasoning if necessary.