First Step: Prepare the Ingredients Gather all ingredients: cooked spaghetti, ground beef, marinara and Alfredo sauces (or homemade ingredients), cheeses, and optional vegetables. Mince garlic, chop onions and peppers if making your own sauce. Measure sauces and cheese for efficient assembly.

Second Step: Cook the Meat and Sauce Heat olive oil in a skillet over medium heat. Sauté onions and green bell peppers until translucent. Add minced garlic and cook for 1–2 minutes until fragrant. Add ground beef, cooking until no longer pink, draining excess fat. Season with salt, pepper, and Italian seasoning. Stir in marinara sauce and simmer for about 5 minutes to combine flavors.

Third Step: Cook the Spaghetti Boil salted water in a large pot and cook spaghetti according to package instructions until al dente. Drain well and set aside.

Fourth Step: Prepare Alfredo Sauce (if homemade) In a saucepan, melt butter over medium heat and sauté minced garlic for about 1 minute. Stir in flour and cook for 1 minute while stirring. Remove from heat and gradually whisk in heavy cream until smooth. Return to heat and stir continuously until thickened. Add freshly grated Parmesan cheese and stir until melted and creamy.

Fifth Step: Assemble the Casserole Layers

1. Lightly grease a 9×13-inch baking dish.
2. Spread half of the cooked spaghetti evenly in the dish.
3. Layer half of the meat marinara sauce on top.
4. Pour half of the Alfredo sauce over the meat sauce and spread evenly.
5. Sprinkle half of the shredded mozzarella and grated Parmesan cheese.
6. Repeat layering with remaining spaghetti, meat sauce, Alfredo sauce, and cheeses.

Final Step: Bake and Serve Bake uncovered at 350-375°F (177-190°C) for 20–30 minutes until cheese is melted, bubbly, and golden brown. Let cool for 5–10 minutes before serving to allow flavors to meld and casserole to set for easy serving.