Heat the oven to 350 degrees. In a mixing bowl, combine the ground beef, egg, 1/2 cup finely chopped Vidalia onion, milk, Worcestershire sauce, salt, black pepper, and garlic powder. Mix until evenly blended.
Shape the mixture into a loaf and place it in a loaf pan. Bake for 45 minutes until the internal temperature reaches 160 degrees.
While the meatloaf bakes, melt the butter in a skillet over medium heat. Add the sliced Vidalia onions and cook, stirring often, until they soften and turn light golden, about 10 minutes.
Sprinkle the flour over the onions and stir for one minute. Slowly pour in the beef broth while stirring to avoid lumps. Simmer until the gravy thickens, about 5 minutes. Season with a pinch of salt and pepper if needed.
Remove the meatloaf from the oven and let it rest for 5 minutes. Slice and serve with the warm Vidalia onion gravy spooned on top.