Preheat your oven or grill to 350°F and line a baking sheet with foil.

Melt 1 tablespoon of butter in a sauté pan over medium heat. Add the diced onion and cook until fragrant and slightly brown, about 3-5 minutes. Stir in the minced garlic and cook for another 2-3 minutes before removing from heat.

In a large bowl, combine the ground beef, egg, bread crumbs, milk, Worcestershire sauce, dried thyme, and sautéed onion and garlic mixture. Mix together, being careful not to overwork the meat. Divide into six equal portions and shape into patties.

Wrap a slice of bacon around the edge of each meat patty, securing the ends if necessary.

In a bowl, whisk together the ketchup, brown sugar, and spicy brown mustard. Spread the mixture over the tops of each meatloaf and sprinkle with fried onion pieces.

Bake on the prepared baking sheet until the bacon is golden and crispy, about 1 hour and 15 minutes, ensuring an internal temperature of 160°F.