1-First Step: Get the oven and pasta water ready Preheat your oven to 375°F so it is ready when the pasta is mixed and assembled. Set a large pot of water on the stove and salt it heavily. This helps the spaghetti taste better from the inside out. Once the water comes to a boil, add 1 pound dried spaghetti noodles and cook them for 1 minute less than al dente. This small step matters because the pasta will keep cooking in the oven. If you cook it all the way through now, the final dish can turn soft or mushy.

2-Second Step: Make the creamy Alfredo sauce While the pasta cooks, melt 3 tablespoons unsalted butter in a large pot over medium heat. Whisk in 3 tablespoons all-purpose flour and cook it until it turns golden brown. This helps remove the raw flour taste and gives the sauce a better flavor. Next, slowly whisk in 3 cups whole milk or 2 percent milk and 1 cup heavy cream. Add the liquid gradually so the sauce stays smooth. Bring it to a boil, then lower the heat and let it simmer until thickened. This milk-heavy cream combo is what gives Alfredo Baked Spaghetti its silky, rich texture.

3-Third Step: Add the cheese and seasonings Stir in 4 ounces of the shredded mozzarella, 3 ounces of the Parmesan, 1/2 teaspoon garlic powder, and 1 teaspoon kosher salt. Keep stirring until the cheese melts fully and the sauce turns smooth. The sauce should look creamy and glossy, not grainy. If the sauce seems too thick, add a splash of milk. If it seems too thin, let it simmer a little longer. Freshly grated Parmesan works best because it melts better and gives stronger flavor than pre-shredded cheese.

4-Fourth Step: Combine the pasta and sauce Drain the spaghetti well, then add it directly into the sauce pot. Toss gently until every strand is coated. Take your time here so the sauce spreads evenly through the pasta. If you are adding vegetables such as spinach, mushrooms, or broccoli, this is a good point to mix them in. They should already be cooked or steamed, since the baking time is short and mostly meant to heat the dish through.

5-Fifth Step: Assemble and bake Transfer the sauced spaghetti to a baking dish. Spread it out evenly so the cheese on top melts in the same way across the dish. Sprinkle on the remaining mozzarella and Parmesan. Bake at 375°F until the top is bubbling and browned. The exact time can vary a bit depending on the depth of your baking dish, but most casseroles will look ready once the edges are hot and the cheese has melted into a golden layer.

6-Final Step: Rest and serve Let the Alfredo Baked Spaghetti rest for a few minutes after baking. This short pause helps the sauce settle, so it is easier to scoop and serve. Finish with finely chopped parsley leaves if you want a fresh look and a little color on top.