INGREDIENTS
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3 1/2 to 4 pounds meaty beef bones, cut into 2- to 3-inch pieces
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2 tablespoons vegetable oil
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3/4 cup dry red wine
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2 1/2 cups low-sodium beef broth
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1 teaspoon kosher salt, plus more for seasoning
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1/8 teaspoon freshly ground black pepper, plus more for seasoning
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6 tablespoons unsalted butter (3/4 stick), at room temperature
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6 sweet French sandwich rolls, sliced in half horizontally
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Kosher salt
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Freshly ground black pepper
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1 1/2 pounds thinly sliced roast beef
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Horseradish Mayonnaise, for serving (optional; see recipe intro)