Preheat the oven to 425°F and start boiling water for the pasta. Cook pasta according to package directions.
For the salmon: Pat salmon fillets dry with a paper towel. Place them on a parchment paper lined baking sheet. In a small bowl, combine melted butter and blackened seasoning. Brush mixture over salmon on all sides. Bake at 425°F for 10-12 minutes or until the salmon is cooked through and flakes easily with a fork.
For the sauce: In a large skillet over medium-low heat, melt ½ cup of butter. Add the minced shallot and garlic and sauté for 1-2 minutes until fragrant. Whisk in the heavy cream, parmesan cheese, and Cajun seasoning. Whisk until well combined and let it simmer for 5-8 minutes, stirring occasionally. The sauce will thicken as it cools.
Add the cooked pasta to the skillet with the sauce, tossing to coat. Note: Add 1 Tablespoon of reserve pasta water at a time until the pasta is coated in the sauce and the desired consistency is reached. Discard any unused water.
Top the Cajun pasta with salmon and garnish with chives and a lemon wedge, if desired.
Notes
I don't add extra salt and pepper to this dish because most Cajun seasoning already contains it. Taste and season to your preference.
For crispy salmon: Broil for the final 2-3 minutes of baking. Keep an eye on it to prevent burning. Salmon should be cooked to an internal temperature of 145 degrees Fahrenheit.
I recommend using freshly grated parmesan as it melts better and creates a smoother, creamier sauce compared to pre-shredded cheese.
Reserve ¼ cup of pasta water. Add 1 Tablespoon of pasta water at a time until the pasta is coated in the sauce and the desired consistency is reached. Discard any unused water.
Garnish the dish with fresh parsley or chives and a squeeze of lemon juice, if desired.