Preheat the oven to 350 F. Cook the spaghetti and drain. Return to pot and add eggs, parmesan cheese, butter and salt & pepper (to taste). Mix well. Place pasta mixture in greased pie pan, pressing down slightly to form a “crust”. Spread mascarpone over pasta and top with meatball halves. Pour marinara sauce over meatballs and sprinkle with mozzarella cheese. Cover with foil (spray foil with cooking spray to avoid sticking) and bake for 20-25 minutes at 350 degrees. Remove from the oven, let sit for 5- 10 minutes, and then cut into slices and serve.