In a large bowl, crumble the ground beef into small pieces, then sprinkle in the dry onion soup mix, breadcrumbs, and Parmesan cheese.
In a separate bowl, mix together the beaten egg, beef broth, ketchup, and Worcestershire sauce. Once combined, pour the mixture into the large bowl with the ground beef and combine everything together.
Transfer the meatloaf mixture into a bread loaf pan lined with aluminum foil. Press firmly to form the meatloaf into an even loaf.
Prepare the glaze by mixing the ketchup and balsamic vinegar together in a small bowl, then paint the glaze over the top of the meatloaf.
Place the meatloaf in the oven for 1 hour, or until the interior reaches 160 degrees. Remove from the oven, and let cool briefly, then serve.
Notes
Make ahead: You can form the meatloaf in advance and bake it the next day if desired.