Preheat your oven to 375°F (190°C). In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, onion, garlic, salt, and pepper. Mix until just combined.

Roll the meat mixture into golf ball-sized meatballs and place on a parchment-lined baking sheet.

Heat olive oil in a skillet over medium heat. Once hot, add the meatballs in batches and sear until golden-brown, about 5 minutes per side.

In the same skillet, add more olive oil if needed and sauté the chopped onion until translucent, around 3 minutes. Add minced garlic and tomato paste, cooking for another minute.

Pour in the red wine and beef broth, scraping any browned bits from the bottom of the skillet. Bring to a gentle simmer.

Return the meatballs to the skillet, covering them with the gravy. Cover and simmer on low heat for about 30 minutes.