Preheat oven to 350°F. Grease 9x13-inch baking dish with nonstick spray.
Cook spaghetti to al dente according to package directions; drain and return to pot. Stir in the butter until melted, add 1/2 cup Parmesan and stir until noodles are coated.
Meanwhile, as the spaghetti is boiling, brown the beef in a large skillet over medium heat, crumbling as it cooks; drain excess grease. Stir in pasta sauce and heat 5 more minutes.
In a medium bowl, combine the Ricotta, egg and remaining 1/2 cup Parmesan; set aside.
To assemble the casserole, spread 1/2 cup of the meat sauce in the bottom of the prepared baking dish. Spread the cheese coated spaghetti into the pan, pushing to all corners. Layer Ricotta mixture evenly over the spaghetti and then top with remaining sauce. Sprinkle evenly with mozzarella cheese.
Cover with foil. Bake 30 minutes. Remove foil, bake 10 more minutes, until cheese is melted.
Pasta: Our favorite is spaghetti, but you can use other pasta shapes in the recipe like rigatoni, rotini, ziti, etc.
Sauce: Instead of layering the meat sauce, try mixing it into the noodles if you prefer a more even coating on the spaghetti. If you like your baked spaghetti saucy, add even more sauce. I sometimes add up to 32 ounces.
Veggies: Saute veggies like bell peppers, mushrooms, onions, eggplant, and zucchini with the meat for added heartiness. Or, stir in fresh spinach leaves to the meat sauce.
Meat: Lighten this dish with ground turkey instead of beef. Or, mix up the flavor with Italian sausage or pepperoni!
Cheese: Not a fan of Ricotta? Try cottage cheese! Want to mix up the mozzarella? Try provolone or fontina instead!
Halve: Feeding a smaller family? Make two 9x9's or 8x8's instead of one big 9x13 so you can freeze one for later.
Nutrition information is an estimate only based on 1 serving = 1/8th of pan.