In a large mixing bowl, combine the ground beef, breadcrumbs, 1/4 cup grated Parmesan, chopped parsley, minced garlic, egg, salt, and pepper. Mix until just combined to keep meatballs tender.
Shape the mixture into small, bite-sized meatballs about 1 inch in diameter. Set aside on a plate.
Bring a large pot of salted water to a boil. Add penne pasta and cook until just al dente, about 1-2 minutes less than package instructions. Drain and set aside.
In a medium saucepan, gently heat the heavy cream over medium-low heat. Stir frequently until it begins to simmer. Remove from heat and stir in half of the shredded mozzarella cheese until melted and smooth.
Lightly grease baking dish with olive oil. Spread cooked pasta evenly in the dish. Nestle raw meatballs evenly throughout the pasta. Pour creamy Alfredo sauce over pasta and meatballs, coating everything well.
Sprinkle remaining mozzarella and 1/2 cup grated Parmesan cheese evenly over the top.
Place baking dish in preheated oven at 375°F (190°C). Bake uncovered for 25-30 minutes, until meatballs are cooked through and cheese topping is golden and bubbly.
Remove from oven and let cool for a few minutes before serving. Garnish with extra fresh parsley if desired. Enjoy!