Making Cheesy French Onion Meatballs is a straightforward process. Just follow these steps:

1. Preheat Oven: Preheat your oven to 400°F (200°C).
2. Sauté Onions: In a skillet, heat olive oil over medium heat. Add sliced onions and cook until caramelized, about 10 minutes. Stir occasionally.
3. Mix Meatball Ingredients: In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, mozzarella cheese, parsley, minced garlic, eggs, Worcestershire sauce, salt, pepper, and red pepper flakes. Add half of the caramelized onions to this mixture and mix well.
4. Form Meatballs: Shape the mixture into meatballs, about 1 to 1.5 inches in diameter. Place them on a baking sheet lined with parchment paper.
5. Bake Meatballs: Bake in the preheated oven for 20 minutes or until cooked through.
6. Prepare Sauce: In a saucepan, combine the beef broth and the remaining caramelized onions. Bring to a simmer and let it cook for 5 minutes.
7. Add Cheese: Once the meatballs are done baking, place them in the saucepan with the broth and onions. Top with additional mozzarella cheese if desired.
8. Melt Cheese: Cover the saucepan and let it simmer for an additional 5 minutes until the cheese is melted and bubbly.
9. Serve: Remove from heat and let it cool slightly before serving.

Following these steps will ensure you create delicious Cheesy French Onion Meatballs that are sure to impress.