Mix the ground beef well with all the other ingredients for the meatball. Press about two thirds of the meat on the bottom and sides of a large bowl lined with plastic food wrap. This is the mold for the meatball.
Sprinkle the insides all over with mozzarella before putting in the spaghetti. Then pour some tomato sauce on top of it.
Now shape the rest of the meat into a ball and press it into a large, flat circle which you will use to cover the filling. Pinch the edges of the circle together with the rest of meatball.
Turn the bowl upside down onto a baking tray lined with baking parchment. Remove the bowl and the food wrap and bake the meatball for 30 minutes at 340°F. After that, pour the rest of the tomato sauce onto the meatball and sprinkle it with parmesan and chopped basil.