1-First step: Get the oven and pasta water ready Start by arranging your oven racks and preheating the oven to 375°F. This gives the casserole the right heat so the cheese melts evenly and the top gets lightly browned. At the same time, bring a large pot of salted water to a boil. Salted water matters because it seasons the pasta from the inside out, which helps the final dish taste fuller. Once the water is boiling, cook 1 pound of dried spaghetti for 1 minute less than al dente, following the package directions. This is important for any baked spaghetti recipe because the noodles will keep cooking in the oven. If you cook them too long at this stage, they can turn soft and mushy after baking.

2-Second step: Make the Alfredo-style sauce In a large pot, melt 3 tablespoons of unsalted butter over medium heat. When the butter is melted, whisk in 3 tablespoons of all-purpose flour. Keep whisking and cook the mixture until it turns golden, which usually takes about 1 to 2 minutes. This cooked butter and flour base is what gives the sauce its smooth, creamy body. Slowly whisk in 3 cups of whole milk or 2 percent milk, then add 1 cup of heavy cream. Adding the liquid gradually helps prevent lumps. Bring the mixture to a boil, then lower the heat and simmer for about 5 to 7 minutes until the sauce thickens. The milk-cream combo is what gives Alfredo Baked Spaghetti its velvety texture, so do not rush this part.

3-Third step: Add the cheese and seasoning Remove the pot from the heat before adding the cheese. Whisk in most of the 6 ounces of low-moisture mozzarella, along with most of the 4 ounces of finely grated Parmesan. Then stir in 1/2 teaspoon garlic powder and 1 teaspoon kosher salt. The sauce should look smooth, thick, and glossy. If you want a stronger cheese flavor, you can add a little more Parmesan on top later. For the best result, use freshly grated Parmesan instead of shelf-stable grated cheese. Fresh cheese melts better and avoids a gritty texture. This step is what gives the casserole its classic Alfredo taste while keeping it easy for home cooks.

4-Fourth step: Toss the pasta with the sauce Drain the spaghetti well, then add it directly to the cheese sauce. Toss until every strand is coated. The goal is to give the noodles enough sauce so that each bite stays creamy after baking. If the mixture seems very thick, you can add a small splash of milk to loosen it slightly. This is where the dish starts to feel like a proper spaghetti casserole. The pasta should look generously coated, not dry. If you are making a lighter version, this is also the point where you can stir in extra cooked vegetables like spinach or broccoli.

5-Fifth step: Assemble and bake Transfer the coated pasta to a greased baking dish. Spread it out evenly so it bakes at the same pace across the pan. Sprinkle the remaining mozzarella and Parmesan over the top. This top layer melts into a golden, bubbling finish that makes Alfredo Baked Spaghetti so appealing when it comes out of the oven. Bake at 375°F for about 20 minutes, or until the casserole is hot, bubbling, and the cheese has melted. If you want a little more browning on top, broil it briefly at the end. Keep a close eye on it during broiling because the cheese can brown quickly.

6-Final step: Rest, garnish, and serve Let the baked spaghetti cool for a few minutes before serving. This short rest helps the sauce settle, so the portions hold together better. Finish with finely chopped parsley leaves if you want a pop of color and a fresh note. Then serve warm and creamy.