French Dip Sandwich

Ingredients

• 3.5 pounds beef bone marrow cut into 2- to 3-inch pieces
• 6 servings pepper black freshly ground
• 0.8 cup wine dry red
• 6 servings kosher salt 
• 2.5 cups beef broth low-sodium
• 1.5 pounds roast beef thinly sliced
• 6  sandwich rolls sweet french sliced in half horizontally
• 6 tablespoons butter unsalted at room temperature ()
• 2 tablespoons vegetable oil 

Equipment

• bowl
• frying pan
• baking sheet
• sauce pan
• oven
• wire rack
• pot
• sieve
• wooden spoon
• dutch oven
• tongs

Directions

1. For the jus:Season the beef bones with salt and pepper.
2. Heat the oil in a Dutch oven or large, heavy-bottomed pot over medium-high heat until shimmering.
3. Add half of the bones and sear until golden brown on all sides, adjusting the heat as needed so the bottom of the pan doesn’t burn, about 6 to 8 minutes total.
4. Remove the bones to a large plate and repeat with the remaining bones.
5. Add the wine, scrape up any browned bits from the bottom of the pan with a wooden spoon, and simmer until the wine is reduced by half, about 3 to 4 minutes.Return the bones and any accumulated juices on the plate to the pot.
6. Add the broth, measured salt, and measured pepper and bring to a boil. Reduce the heat to low, cover with a tightfitting lid, and simmer until the jus has a deep beefy flavor, about 15 minutes. Uncover, increase the heat to medium, and simmer until the liquid is reduced to about 2 1/2 cups, about 10 minutes.
7. Remove and discard the bones. Set a fine-mesh strainer over a medium saucepan.
8. Pour the jus through the strainer and discard the contents of the strainer.
9. Heat the oven to broil and arrange a rack in the middle.
10. Spread the butter on the cut sides of the rolls and season with salt and pepper.
11. Place the rolls butter-side up on a baking sheet and broil until golden brown and toasted, about 2 minutes.
12. Place the baking sheet on a wire rack.Divide the roast beef into 6 portions. Using tongs, dip 1 portion into the warm jus and place on a roll. Repeat with the remaining portions of roast beef. Close each sandwich and slice in half.Divide the remaining jus among 6 small bowls.
13. Serve with the sandwiches and horseradish mayonnaise, if using.