To prepare the meatballs, preheat the oven to 375°F. Lightly grease a baking sheet with cooking spray or oil.

In a large mixing bowl, combine ground beef, onion, breadcrumbs, Parmesan cheese, eggs, garlic, parsley, basil, salt and pepper. Mix with a fork until combined. Using a spoon or scoop, roll meat into small 1-inch balls. Repeat with remaining meat and arrange on baking sheet.

Bake for 13 to 15 minutes, or until meatballs are almost cooked through.

When the meatballs are cooking, prepare the pasta according to the package instructions.

After the meatballs and pasta are done cooking, layer the pasta and meatballs in a large rectangular baking dish (about 9 inches x 13 inches). Sprinkle with chopped spinach.

In a medium bowl, stir together marinara sauce and heavy cream. Pour sauce over pasta with spinach and meatballs. Sprinkle with mozzarella cheese and extra Parmesan cheese, as desired. Bake in the oven until bubbly and heated through, about 15 to 20 minutes. Garnish with basil, as desired. Serve immediately.