In a large skillet over medium heat, cook the ground beef and chopped onion together, breaking the meat apart as it cooks until the beef is no longer pink and the onion is soft and translucent. Season generously with salt, pepper, and garlic powder.

Add the tablespoon of Worcestershire sauce to the skillet, stir and cook for another minute to deepen the flavor. Remove from heat.

Prepare a 9×13 baking dish with cooking spray. Spread half of the buttered bread cubes across the bottom of the dish in an even layer. Spoon half of the cooked beef mixture over the bread and lay four slices of Swiss cheese over the beef. Repeat with the remaining bread, beef, and Swiss cheese.

Pour the two cups of beef broth evenly over the casserole.

Cover the dish tightly with foil and bake at 375°F for 30 minutes.

Remove the foil and return the casserole to the oven for an additional 15 to 20 minutes until the cheese on top is melted, golden, and bubbling. Allow it to rest for 5 minutes before serving.