Preheat the oven to 400°F (200°C).

In a large bowl, mix together the ground beef, minced garlic, onion powder, chopped parsley, egg, breadcrumbs, Italian seasoning, salt, and pepper.

Shape the mixture into meatballs and place them on a baking sheet.

Bake the meatballs in the preheated oven for 20 minutes or until cooked through.

In a large skillet, heat olive oil and butter over medium heat.

Add the sliced onions and cook until caramelized, about 15-20 minutes, stirring frequently.

Sprinkle the flour over the onions and stir for a minute, then slowly add the beef broth, Worcestershire sauce, and sugar.

Bring the mixture to a boil, then reduce to a simmer.

Add the cooked meatballs to the onion sauce and let it simmer for an additional 10 minutes.

Serve the meatballs and sauce topped with Gruyere or Swiss cheese and grated Parmesan cheese.