Preheat your oven or grill to 350 degrees F (175 degrees C). Line a baking sheet with foil for easy cleanup.
In a sauté pan, melt the butter over medium heat. Add the diced onion and cook until fragrant and slightly browned, stirring occasionally, for about 3-5 minutes. Reduce the heat to low and add the minced garlic, cooking for an additional 2-3 minutes. Remove from heat.
In a large bowl, combine the ground beef, egg, bread crumbs, milk, Worcestershire sauce, thyme, and the cooked onions and garlic. Mix well with your hands, ensuring not to overwork the meat. Divide the mixture into six equal-sized portions and shape them into disks.
Wrap one bacon slice around the edge of each disk, ensuring that the bacon ends just meet or slightly overlap.
In a separate bowl, combine the ketchup, brown sugar, and spicy brown mustard. Divide the mixture equally and spread it over the tops of the mini meatloaves. Sprinkle the crispy fried onions on top.
Bake in the preheated oven or grill for approximately 1 hour and 15 minutes, or until the bacon turns golden and crispy.
Serve these delectable Bacon-Wrapped Mini Meatloaves warm and enjoy the delightful combination of flavors and textures!