Step 1: Mix the meatball ingredients - In a large bowl, add the ground beef, parmesan and cheddar cheese, some of the mozzarella cheese, salt, paprika, black pepper, onion powder, fresh basil, minced garlic, and the egg. Use clean hands to gently mix everything together until fully combined. Try not to overwork the meat, as that can make the meatballs dense instead of tender.
Step 2: Form the meatballs - Use a scoop or your hands to portion the mixture into evenly sized meatballs. A number 20 scoop works great if you have one. Roll each portion between your palms to form smooth, round meatballs.
Step 3: First bake - Place the meatballs in an oven safe baking dish, leaving a little space between each one. Bake at 200°C or 392°F for about 15 minutes. This first bake helps them set and start to cook through.
Step 4: Add sauce and cheese - Carefully turn each meatball over. Spoon the marinara sauce over the top so the meatballs are nicely coated. Sprinkle the remaining mozzarella cheese over everything so it melts down into all the little spaces between the meatballs.
Step 5: Final bake - Return the dish to the oven and bake for another 10 minutes, or until the cheese is melted and lightly golden and the meatballs are cooked through.
Step 6: Serve and enjoy - Remove the casserole from the oven and let it rest for a few minutes. Garnish with extra fresh basil if you like. Serve hot with mashed potatoes, pasta, or a simple veggie on the side.