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1
Season the beef bones with salt and pepper.
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2
Heat the oil in a Dutch oven or large, heavy-bottomed pot over medium-high heat until shimmering.
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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 doesnt burn, about 6 to 8 minutes total.
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4
Remove the bones to a large plate and repeat with the remaining bones.
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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.
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6
Return the bones and any accumulated juices on the plate to the pot.
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7
Add the broth, measured salt, and measured pepper and bring to a boil.
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8
Reduce the heat to low, cover with a tightfitting lid, and simmer until the jus has a deep beefy flavor, about 15 minutes.
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9
Uncover, increase the heat to medium, and simmer until the liquid is reduced to about 2 1/2 cups, about 10 minutes.
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10
Remove and discard the bones.
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11
Set a fine-mesh strainer over a medium saucepan.
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12
Pour the jus through the strainer and discard the contents of the strainer.
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13
Let the jus sit until the fat rises to the surface, about 5 minutes.
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14
Using a spoon, skim off and discard the fat.
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15
Taste and season with additional salt and pepper as needed; keep warm over low heat.
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16
Heat the oven to broil and arrange a rack in the middle.
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17
Spread the butter on the cut sides of the rolls and season with salt and pepper.
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18
Place the rolls butter-side up on a baking sheet and broil until golden brown and toasted, about 2 minutes.
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19
Place the baking sheet on a wire rack.
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20
Divide the roast beef into 6 portions.
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21
Using tongs, dip 1 portion into the warm jus and place on a roll.
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22
Repeat with the remaining portions of roast beef.
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23
Close each sandwich and slice in half.
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24
Divide the remaining jus among 6 small bowls.
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25
Serve with the sandwiches and horseradish mayonnaise, if using.
