In a medium saucepan, combine beef broth, Worcestershire sauce, and garlic powder. Bring to a simmer over medium heat.
Add the roast beef slices to the warm broth and heat through for 3-4 minutes, just until warmed. Season with salt and pepper.
While the beef warms, butter the insides of the hoagie rolls and toast them in a skillet or under the broiler until golden brown.
Using tongs, remove the beef from the broth and divide evenly among the toasted rolls. Reserve the broth for dipping.
Top each sandwich with 2 slices of provolone cheese. Place under the broiler for 1-2 minutes until cheese melts.
Serve immediately with small bowls of the warm au jus for dipping. Enjoy!