Ingredients:

  • 2 large yellow onions, thinly sliced (approximately 400g / 14 oz)
  • 2 tablespoons unsalted butter (30g / 1 oz)
  • 1 tablespoon olive oil (15ml / 0.5 fl oz)
  • 1/2 teaspoon granulated sugar (2g / 0.07 oz)
  • 1/4 teaspoon salt (1g / 0.03 oz)
  • 1/4 cup dry red wine (optional, but recommended - 60ml / 2 fl oz)
  • 1 tablespoon balsamic vinegar (15ml / 0.5 fl oz)
  • 1 pound ground beef (80% lean) (450g / 1 lb)
  • 1/2 pound ground pork (225g / 0.5 lb)
  • 1/2 cup panko breadcrumbs (40g / 1.4 oz)
  • 1/4 cup grated Parmesan cheese (20g / 0.7 oz)
  • 1 large egg, lightly beaten (approx 50g / 1.8 oz)
  • 2 cloves garlic, minced (approximately 6g / 0.2 oz)
  • 1 tablespoon Worcestershire sauce (15ml / 0.5 fl oz)
  • 1 teaspoon dried thyme (2g / 0.07 oz)
  • 1/2 teaspoon dried rosemary (1g / 0.03 oz)
  • Salt and freshly ground black pepper, to taste
  • 4 ounces Gruyère cheese, shredded (approximately 115g / 4 oz)
  • Optional: fresh parsley, chopped for garnish

Instructions:

  1. Melt butter and olive oil in a large skillet over medium-low heat. Add onions, sugar, and salt. Cook, stirring occasionally, until onions are deeply golden brown and caramelized (about 20-25 minutes). Add red wine and balsamic vinegar, scraping up any browned bits from the bottom of the pan. Cook until liquid is mostly evaporated. Remove from heat and let cool slightly.
  2. In a large bowl, combine ground beef, ground pork, panko breadcrumbs, Parmesan cheese, egg, garlic, Worcestershire sauce, thyme, rosemary, salt, and pepper. Gently mix until just combined (do not overmix).
  3. Gently fold in about half of the caramelized onions into the meatball mixture. Use an ice cream scoop or spoon to form meatballs (approximately 1-inch in diameter).
  4. Preheat oven to 375°F (190°C). Place meatballs on a baking sheet lined with parchment paper (optional). Bake for 20-25 minutes, or until meatballs are cooked through and reach an internal temperature of 165°F (74°C).
  5. Remove meatballs from the oven. Top each meatball with shredded Gruyère cheese. Return to the oven and bake for another 2-3 minutes, or until the cheese is melted and bubbly.
  6. Garnish with fresh parsley (optional) and serve immediately.