Heat the oven to 350°F (175°C). Grease a 9-inch deep-dish pie plate or springform pan with some of the olive oil, making sure the bottom and sides are coated.

Cook the spaghetti in salted boiling water until just al dente according to the package directions. Drain it well without rinsing, since the remaining surface starch helps the egg-and-cheese mixture cling to the noodles.

While the pasta cooks, heat the olive oil in a large skillet. Add the chopped onion and ground beef, cooking for about 5–7 minutes while breaking up the meat until it is browned; drain excess fat if necessary.

Add the minced garlic and cook for 30 seconds, just until fragrant. Stir in the marinara sauce and Italian seasoning, then simmer for 8–10 minutes so the sauce thickens slightly and the flavors come together.

Toss the warm, drained spaghetti with the melted butter, lightly beaten eggs, 1/4 cup of Parmesan, salt, and black pepper. Mix thoroughly so the noodles are coated, but handle them gently to keep them from breaking.

Transfer the spaghetti mixture to the prepared pan and press it firmly across the bottom and up the sides. Shape a shallow center well for the filling, taking care to create an even crust that will support the saucy layers.

Spread the ricotta or small-curd cottage cheese evenly over the spaghetti base. Sprinkle about 1/2 cup of the shredded mozzarella over the creamy cheese layer.

Spoon the warm meat sauce over the cheese, spreading it gently toward the edges without disturbing the spaghetti crust. Finish with the remaining mozzarella and Parmesan.

Bake the pie uncovered at 350°F (175°C) for 35–40 minutes. It is ready when the cheese is melted and lightly browned and the center is hot.

Let the baked spaghetti pie rest for 10 minutes before slicing. Use a sharp knife to cut it into wedges, then lift each serving carefully so the layers remain intact.