In a large skillet, melt 2 tablespoons of salted butter with 1 tablespoon of olive oil over medium heat. Add 3 sliced sweet onions, sprinkle with sea salt, coarse black pepper, and a pinch of granulated sugar. Sauté for 20-30 minutes until the onions turn a golden brown and caramelize.

In a large mixing bowl, combine 1 pound of ground beef, ½ cup of Italian-style breadcrumbs, ½ cup of whole milk, 1 large egg, a packet of French onion soup mix, and 2 tablespoons of Worcestershire sauce. Once your caramelized onions have cooled slightly, stir in half of them into the meat mixture until just combined.

Shape the meat mixture into a loaf that fits in your crockpot. Place it at the bottom of your slow cooker, ensuring it sits level. Top with the remaining caramelized onions.

Cover the crockpot with its lid and set it to low heat for 6-8 hours or high heat for 3-4 hours until it reaches an internal temperature of 160°F.

In the last 30 minutes of cooking, carefully lift the lid and layer 4-6 slices of Swiss cheese on top. Cover again and continue cooking until the cheese is melted and bubbly.

Once cooked, transfer the meatloaf to a cutting board and let it rest for about 10 minutes. Serve warm, garnished with fresh thyme, alongside mashed potatoes or crusty bread.