Preheat oven to broil. Cut bread loaf in half horizontally, place the halves on a baking sheet cut side up and toast them in the oven until light brown, 1 to 2 minutes.
Spread horseradish on the bottom half of the loaf, then layer on roast beef.
To make the jus, mix reconstituted Kitchen Accomplice Beef Broth Concentrate or Beef Bone Broth Concentrate and Worcestershire sauce in a small bowl. Baste top half of bread with 1/4 cup of the jus. Place top half of the bread over roast beef to complete sandwich. Cut the sandwich in four pieces and serve with the remaining jus for dipping.
