1. Preheat oven to 350°F (175°C).
2. Sauté onions in olive oil until translucent; add minced garlic and cook for another minute.
3. In a bowl, mix ground beef, breadcrumbs, eggs, sautéed onions and garlic, salt, and pepper until well combined.
4. Shape the mixture into a loaf on a lined baking sheet or in a loaf pan.
5. Whisk together balsamic vinegar, ketchup, brown sugar, salt, and pepper; spread half over the meatloaf.
6. Bake for about 1 hour or until internal temperature reaches 160°F (70°C), glazing with remaining sauce in the last ten minutes.
