Step 1

Place a Dutch oven or large skillet over medium-high heat. Make sure the Dutch oven or skillet is large enough to toss the pasta in.

Step 2

When the pan is hot, add the olive oil, the sliced fennel, and the onion.

Step 3

Add the kosher salt and stir.

Step 4

Cover the Dutch oven and let the mixture cook down until the fennel and onion are softened and translucent, about 10 minutes.

Step 5

Remove the lid and adjust the heat to low.

Step 6

Stir in the butter.

Step 7

Continue to sauté the mixture until deeply brown and very soft, about 35-40 minutes.

Step 8

Remove the Dutch oven from the heat.

Step 9

About 10 minutes before the fennel and onions are cooked, set a large pot of heavily salted water to boil.

Step 10

Season both sides of the salmon filet with the kosher salt and black pepper.

Step 11

Place a separate skillet over high heat.

Step 12

Add the canola oil, swirling to coat the pan.

Step 13

When the skillet is just beginning to smoke, add the salmon and sear, depending on the thickness of the salmon, until medium-rare at 145 degrees F, about 3-5 minutes on each side.

Step 14

Transfer the salmon to a clean cutting board to rest, and reserve until ready to plate.

Step 15

When the water is boiling, add the pasta.

Step 16

Boil until about 2 minutes shy of al dente according to package directions, about 8 minutes 30 seconds.

Step 17

Reserve 2 1/2 cups of the starchy pasta water.

Step 18

Drain the pasta into a colander.

Step 19

Set the pot with the fennel & onion mixture over medium-low heat on the stove-top.

Step 20

Add the heavy cream, red pepper flakes, and the black pepper, stirring to combine.

Step 21

Bring the mixture to a boil, and simmer until slightly reduced and thickened, about 4-5 minutes.

Step 22

Add the drained pasta, along with the lemon zest and 2 cups of the reserved starchy pasta water, tossing to combine.

Step 23

Keep the pasta moving constantly until the sauce is glossy and thick, about 4-5 minutes. If the sauce becomes too dry, add splashes of pasta water as necessary.

Step 24

Add the lemon juice while tossing and stir to fully combine.

Step 25

Taste, and adjust for salt as needed.

Step 26

Spoon the pasta into bowls while hot.

Step 27

Flake off large chunks of the seared salmon and sprinkle over the top of each bowl.

Step 28

Sprinkle with black pepper and red pepper flakes, and top with the reserved fennel fronds and additional lemon zest.

Step 29

Serve