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1
Heat 2 tablespoons oil in heavy large skillet over medium-high heat.
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2
Add onions and saute until deep golden brown, about 28 minutes.
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3
Set aside.
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4
Boil cream and clam juice in heavy large saucepan until reduced to 1 cup, about 15 minutes.
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5
Remove from heat.
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6
Whisk in horseradish.
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7
Season sauce to taste with salt and pepper.
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8
(Caramelized onions and sauce can be prepared 1 day ahead. Cover separately and refrigerate.)
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9
Cook broccoli rabe in large pot of boiling salted water until crisp-tender, about 2 minutes.
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10
Using tongs, transfer to plate.
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11
Reserve cooking water.
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12
Cut broccoli rabe lengthwise in half, then chop coarsely crosswise.
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13
Return water in pot to boil.
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14
Add pasta and cook until tender but still firm to bite, stirring occasionally.
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15
Drain, reserving 1 cup cooking liquid.
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16
Return pasta to same pot.
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17
Add 2 tablespoons oil, caramelized onions, broccoli rabe, Parmesan cheese, and 3/4 cup reserved cooking liquid.
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18
Toss pasta mixture over medium-high heat until heated through, adding remaining reserved cooking liquid if pasta is dry, about 5 minutes.
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19
Season pasta to taste with salt and pepper.
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20
Meanwhile, sprinkle salmon with salt and pepper.
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21
Heat remaining 2 tablespoons oil in heavy large skillet over high heat.
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22
Add salmon to skillet, skin side up, and cook until brown on bottom, about 3 minutes.
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23
Turn salmon over and cook until skin is golden brown and crisp and salmon is just opaque in center, about 3 minutes longer.
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24
Bring horseradish sauce to simmer.
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25
Divide pasta mixture among 4 plates.
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26
Top with salmon, skin side down.
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27
Spoon horseradish sauce over salmon and serve.
