Prepare Au Jus as needed.
Slice rolls in half lengthwise- butter each side.
Turn oven onto broil.
When au jus comes to boil, add roast beef, turn heat down.
Put rolls into oven, butter side up. Broil rolls until crispy.
Add roast beef to rolls, pour Au Jus liquid into bowls or cups.
Dip sandwich into Au Jus while eating.