01 -
Melt the butter in a skillet over medium heat. Add the sliced onions and salt, then cook for 15-20 minutes, stirring often, until soft and golden.
02 -
In a large bowl, combine the ground beef, breadcrumbs, milk, eggs, onion soup mix, Worcestershire sauce, garlic powder, pepper, and Parmesan. Mix gently just until combined.
03 -
Make a foil sling in a 6-quart slow cooker. Spread half of the onions over the bottom, then shape the beef mixture into a wide loaf and place it on top.
04 -
Pour the beef broth around the loaf, not over it. Spoon the remaining onions over and around the beefloaf.
05 -
Cover and cook on low for 4-5 hours, until the center of the loaf reaches 160°F on an instant-read thermometer.
06 -
Lay Swiss cheese slices over the top. Cover and cook for 10-15 minutes longer, until the cheese is melted.
07 -
Use the foil sling to lift the loaf out carefully. Rest for 10 minutes, then slice and serve with the onion broth spooned over the top. Garnish with parsley if using.