In a large mixing bowl, combine the ground beef, dry French onion soup mix, crushed French fried onions, milk, egg, salt, and pepper.
Mix the ingredients by hand until just incorporated, ensuring not to overwork the meat which can cause toughness.
Form the mixture into an oval loaf that fits inside your slow cooker.
Pour the beef broth into the bottom of the crockpot to provide moisture and prevent sticking.
Place the meatloaf into the crockpot, cover, and cook on LOW for 6 hours (or HIGH for 3 hours) until the internal temperature reaches 160°F (71°C).
Once cooked, carefully drain any excess grease from the crockpot.
Layer the Swiss cheese slices over the top of the hot meatloaf.
Cover the crockpot for an additional 5 to 10 minutes until the cheese is fully melted.
Allow the meatloaf to rest for 10 minutes before slicing to ensure it holds its shape.