Ultimate French Onion Meatloaf

Ingredients

• 1 lb ground beef (80/20 blend)
• 1 lb ground pork
• 1 cup bread crumbs
• 1 large egg, beaten
• ½ cup milk
• 1 teaspoon garlic powder
• 1 teaspoon onion powder
• 1 teaspoon dried thyme
• ½ teaspoon black pepper
• 1 teaspoon salt
• 1 cup Gruyère cheese, shredded
• 2 medium onions, thinly sliced
• 2 tablespoons unsalted butter
• 1 tablespoon olive oil
• 1 teaspoon sugar
• 1 tablespoon balsamic vinegar (optional)