Preheat oven or grill to 350°F. Line a baking sheet with foil for easy clean up.
Melt 1 tablespoon butter in sauté pan over medium heat. Cook 1 medium onion until fragrant and slightly brown while stirring occasionally, about 3-5 minutes. Reduce heat to low and add 2 cloves garlic, cook for 2-3 minutes. Remove from heat.
In large bowl, combine ground 1 1/2 pounds ground beef, 1 large egg, 1 cup bread crumbs, 1 cup milk, 1 tablespoon Worcestershire sauce, 1 teaspoon dried thyme, and cooked onions and garlic. Use hands to mix well, but try not to over work the meat. Divide into six equal sized portions and shape into thick patties.
Wrap one of the 6 bacon slices around the edge of patty. Diameter of meatloaf should be so that the bacon ends just meet or slightly overlap. If needed, you can use a toothpick to secure the bacon in place. Note: the bacon will shrink as it cooks.
In a separate bowl, combine 1/2 cup ketchup with 1 tablespoon spicy brown mustard and 1 tablespoon brown sugar. Divide equally and spread over the tops of the mini meatloaves. Sprinkle tops with 1/2 cup fried onion pieces.
Bake in preheated oven or grill until bacon is just golden, about 1 hour and 15 minutes, or until an internal thermometer reads 160°F.