Chef John's Beef on Weck Sandwiches

Details

Ingredients

• 2 pounds beef top-sirloin roast
• salt and pepper to taste
• 1 tablespoon vegetable oil
• 2 teaspoons all-purpose flour, or as needed
• 2 ½ cups cold beef broth
• 2 teaspoons aged balsamic vinegar, or to taste
• 4 kummelweck dinner rolls, split
• ¼ cup extra-hot prepared horseradish, or to taste